Blackett-Taylor had impressed since heading to the Toughsheet Stadium in the January window but was forced off during the first half at Rotherham.
“He’s had a scan, unfortunately it’s a serious one. It’s a decent grade, a thigh strain, high up on the tendon, so it’s not going to be a quick fix,” said Schumacher.
“I don’t think we’re 100 per cent sure of the time frame yet but it’ll be a little while because he’ll have to go and see his specialist and all that, and go back to Derby and figure out what the plan is.
“But it’s a serious enough one that he did having that shot on Saturday, so it’s disappointing but it gives an opportunity for someone else.”
Blackett-Taylor has had bad luck with injuries and it is another setback after a promising start with the Whites.
“It’s obviously a big blow because he has made an impact,” Schumacher added. “It was one of them though, he’s that explosive type of player, fast twitch fibres and all that.
“He has an injury history, it’s what’s been tough for him over the years, that’s why he probably hasn’t played as many games as he should have.
“We sort of know that when you’re getting a player like that, and we’ve tried to manage his load, tried to manage his training schedule and all that.
“He didn’t start the week before, came on, made a huge impact and unfortunately it’s one of those things, it is a blow because he’s been good for us.”
Chris Forino was absent from the squad against Doncaster, with skipper Eoin Toal returning to the backline.
“Forino had a little bit of a niggle so we didn’t want to risk him,” the head coach explained. “He had a little bit of a stiff thigh and hip from Saturday’s game, he felt it after about an hour. That’s what I said yesterday in the press, we had one or two we needed to make decisions on.
“Toaly said he’d play through the pain of his ankle, he played. I wanted to freshen Jordi up, he’s played a lot of minutes lately.
“I didn’t think he had the energy that he normally has on Saturday, but he was bright when he came on today. Cyrus stepped in for him.
“And then Johnny Kenny and Demps were brilliant when he came on at half-time on Saturday. So I thought the starting line-up was worthy of what we picked, and the performance in the first half was actually really good.
“Some of the football that we played after a tough opening, because Doncaster were bright, some of the football that we played in the first half was excellent.”