CHESTER — The math presents an intriguing picture for the Philadelphia Union this week.

In his 11 league games as interim manager, Ryan Richter has used only 15 different starters. He has seven players away for the international window, including five regular starters.

Change will have to come for Saturday’s visit from Orlando City. But it won’t be in Richter’s messaging.

“Honestly, we’re not making a big point of it because when I look at the team that we’re going to put out on Saturday, we still have a ton of quality,” Richter said. “So of course we’re missing players, and maybe some guys that haven’t gotten so many minutes lately. But when I look at the group, you’re talking about putting in national team players. You’re talking about putting in players that have a pretty good track record in this league and in other leagues. So I step in with full confidence, and the message is the same.”

Consistency has been arguably the biggest part of Richter’s approach. The Union (10-10-6, 36 points) have rocketed from last place to sixth in the Eastern Conference during an 11-game unbeaten streak (9-0-2) and a five-game winning streak. Both tie franchise records.

From setting his first lineup on July 22 against the Red Bulls, he’s had to a make a total of seven changes week to week. The starting XI he named against Seattle on July 25 has been repeated seven times.

He won’t have that luxury this week. Andre Blake (Jamaica) and Danley Jean Jacques (Haiti) are away along with the American trio of Neil Pierre, Frankie Westfield and Cavan Sullivan. That quintet has made 54 of a possible 55 starts since the World Cup break.

But there aren’t many serious selection quandaries. Andrew Rick will step in for Blake. Jesus Bueno is likely to start for Jean Jacques. Quinn Sullivan replaces his younger brother. The starting forward tandem of Milan Iloski and Bruno Damiani is preserved.

It gets hairy at the back. The Union have only three recognized outside backs in the roster, and deep reserve Philippe Ndinga is also away with Gabon.  They have two reserve center backs in Geiner Martinez and Japhet Sery Larsen, which could move Nate Harriel to right back. But Harriel has been great centrally paired with Pierre.

Richter wasn’t giving any hints about moving Harriel to right back, his more natural position, or keeping him central. That would force someone out of position at fullback, a predilection of predecessor Bradley Carnell that proved calamitous this season.

“We want to give the team consistency. That’s clear,” Richter said. “And one thing that we’re all confident that Nathan can do a great job at center back, like he’s proven over the last couple months, but as he’s proven over the last five years, he’s a great right back as well. So we’re totally confident in the group that we’re putting out there, and Nathan is going to be a key piece no matter what position he lines up in.”

If Richter wants to keep Harriel centrally, it’s possible someone could get a call from Union II, whose season ended last week. Left back Jordan Griffin, 17, is a candidate.

Orlando City (10-12-4, 34 points) is talking through similar struggles.

The Lions are missing five players, including young American Justin Ellis, who leads them with 10 assists, and Tyrese Spicer, the Trinidadian forward who is third on the squad with six goals. Marco Pasalic (Croatia) and Wilder Caratagena (Peru) thin out their midfield, and David Brekalo’s Slovenia call leaves a rickety defense without a reliable piece.

There is a question mark over Antoine Griezmann, the French legend who injured a thigh in an Open Cup loss to Columbus 10 days ago. He was listed as questionable but didn’t play on the turf in last week’s loss to New England, and trained to the side as recently as Wednesday. The Frenchman has eight goals and three assists in 10 games with the club.

Orlando fits a similar trap as last week’s opponent, Sporting KC, one the Union didn’t heed in falling behind by three goals within 16 minutes only to rally for a 4-3 win. Orlando was 12th at the World Cup break, on pace to smash the season record for most goals allowed in a season with 44 through 15 games.

Griezemann’s arrival has improved them and has them up to seventh place. They had been 4-0-1 after the Leagues Cup break before last week’s loss.

“Adding Griezmann is a world-class player that you’re adding to your group. That would make any team better,” Richter said. “It makes them way more dynamic in attack, but overall, much more compact in the way they’re defending. … They look a lot more organized, comfortable defending deeper on the field and keeping their lines tight and making teams break them down, which is difficult for any team to do in this league.”

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With the absence of Cavan Sullivan, who has six goals and eight assists in his last eight games, the contributions of Damiani will be magnified.

Damiani is on a hot streak. After one goal in the league in the first half of the season — and three total in 19 games in all competitions — he has seven goals in his last eight games. He’s scored in three straight games, a stretch in which the Union have scored 14 goals.

“He definitely looks sharper in front of goal,” Richter said. “That’s part confidence, and once it starts rolling, it’s easier to kind of keep that going than to get it going. But also, I think his movement’s been great in the box, too. He’s positioning himself really well and making some pretty good movements to free himself from defenders, and the timing of those movements has been good as well, and he’s arriving at the right time when the cross is about to be played, so he has time to make separation from the defender.

“A lot of the goals have been one-touch finishes. That’s by the movement, by the timing, by the separation he gets, and then also by the service that he’s getting as well.”

Damiani was a similar slow burn last year, with four MLS goals in his first 27 appearances, then three in a four-game span down the stretch.

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Speaking of Ndinga … is frankly not something anyone has been doing around the Union this year.

The U-22 Initiative signing made six appearances with three starts for 220 minutes under Carnell. He was caught up in the morass of struggles that didn’t allow him to properly settle.

A loan move for the 21-year-old old this summer to Zulte Waregem in Belgium broke down after physicals showed a hamstring issue. Ndinga has been recovering on his own in Europe and was healthy enough to get his first call to Gabon’s senior team.

The Union hope to get him back from international duty and reintegrate to the team.

“He’s going to go to Gabon, and then we’ll look to get him back here, and then we’ll reevaluate him and see where he is physically and how he looks, and then start to reintegrate him back into the group,” sporting director Jon Scheer said.

The Union have little outside back depth, so there remains a need for him the rest of the season.

“He’s got a lot of energy and he’s got tools as a player,” Scheer said. “I think what we want to see is consistency and reliability of knowing that as a fullback, yes, he has gifts physically and he can offer high-end plays in moments. But we need to see real clarity and conviction in terms of all phases of play over consistent periods of time.”