PHILADELPHIA — The day after Brad Keller returned from the injured list, Phillies interim manager Don Mattingly saw his highest-paid reliever in the weight room at Great American Ball Park in Cincinnati. Keller was struggling.

“I could tell,” Mattingly said.

The team’s worst fears were realized over the All-Star break when an MRI confirmed that Keller had torn the ulnar collateral ligament in his right elbow. His season is over. The Phillies signed Keller to a two-year, $22 million contract, and that deal might yield only 31 1/3 innings of inconsistent relief work because surgery could keep Keller out for most of 2027 as well.

The injury has major ramifications for how the Phillies will approach the Aug. 3 trade deadline. They have one of the best closers in baseball in Jhoan Duran, and an uncertain bridge to him. There is a good argument that bullpen reinforcements are the club’s greatest need, despite holes in the outfield and rotation.

“With the team in the position that we’re in, you want to come in the second half and fight with the boys,” Keller said. “Just tough to swallow this pill right now.”

For now, a greater focus shifts to José Alvarado, Orion Kerkering and Jonathan Bowlan. Even if the Phillies make a deadline acquisition, several of their current relievers have to assume a more important role. Bowlan, in particular, has impressed with his high-90s fastball and consistent strike-throwing. He was often shuttled back and forth between the majors and minors while with the Kansas City Royals before joining the Phillies in an offseason trade.

They are going to keep testing his resolve.

“His stuff has been good and he’s performing,” Mattingly said. “Bullpens, you always go into the season with some idea who’s your ninth-inning guy, who are your setup guys and things like that. But, for me, bullpens always set themselves because the guys that are pitching well get the ball. And who’s throwing the ball the best gets the ball the most. That’s just the way it works, and that’s what he’s been doing.”

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The Phillies entered the final 65 games with a bullpen that grades well in underlying measurements. It has improved a declining whiff rate from a season ago. It has MLB’s second-highest strikeout rate in 2026 and the seventh-lowest walk rate. It has allowed the third-weakest contact by average exit velocity.

But it ranks 22nd in ERA.

Getting the ball to Duran has been laborious at times. After Duran, Bowlan and Kerkering, who has sometimes struggled to throw strikes, these are the available righties: Max Lazar, Seth Johnson and Chase Shugart.

Internally, the team’s best bullpen prospect is Alex McFarlane. He is 25 and still at Double-A Reading, where he’s posted a 2.12 ERA in 34 innings. He’s carrying a 13 percent walk rate, which is high, but he’s struck out 33 percent of the batters he’s faced. He features a high-90s fastball with tantalizing stuff. He does not have polished command. The Phillies have no idea how he’d react to more stressful situations. They probably need to see soon.

McFarlane is expected to be promoted to Triple-A Lehigh Valley in the near future, according to two team sources who were not authorized to speak publicly.

In the weeks ahead, Phillies president of baseball operations Dave Dombrowski will have to debate what is most pressing to address in a trade. The Phillies could use another outfielder, preferably one who bats right-handed. A fifth starter would help. But the bullpen situation might merit the most attention.

Last summer, the Phillies were in the market for the same items. They traded two top-rated prospects for Duran, who has excelled. They landed Harrison Bader as an outfield buttress.

The Phillies’ two biggest external additions from this past offseason — Keller and Adolis García — are sidelined. That leaves the front office trying to correct the same problems again.

Lacking prospect capital and having various needs could nudge the Phillies toward a measured approach that seeks several marginal upgrades. That is a tactic Dombrowski has often taken at the deadline, the Duran deal being an exception.

Mets lefty reliever A.J. Minter (1.42 ERA in 19 appearances) will likely be traded. (Steph Chambers / Getty Images)

The Phillies’ opponent this weekend, the moribund New York Mets, could be their bullpen trade supplier. The Mets have two left-handed relievers, Brooks Raley and A.J. Minter, who will likely be traded at the deadline. The veterans are both free agents next offseason. They will not command a heavy prospect return, but there will be league-wide interest.

Luke Weaver, a righty setup man who signed for a two-year, $22 million deal, is having an exceptional season. Weaver has 43 strikeouts and 11 walks in 39 innings with a 1.85 ERA. The Mets could opt to keep Weaver for when they plan to contend again in 2027. Or they could sell high now.

Keller’s injury has potential implications beyond 2026. He said he will seek a second opinion with Keith Meister, a leading orthopedic surgeon based in Texas. Even an internal brace procedure, and not the full Tommy John surgery, would probably affect Keller’s availability in 2027.

The Keller situation is similar to one with David Robertson years ago; the Phillies signed him to a two-year, $23 million deal before the 2019 season, and he logged 6 2/3 innings before requiring Tommy John surgery. Even further back, another two-year deal to setup man Mike Adams was derailed by a significant shoulder injury.

Predicting relievers is difficult. The Phillies were burned by one-year deals to Jordan Romano and Joe Ross last season. They took a bigger swing with Keller. But they’re back in the same spot: Feeling a little short in a bullpen that has disappointed them in each of the last three Octobers.

— Brendan Kuty contributed to an earlier version of this report.