The midfielder was sent to the Reds training complex at Melwood for tests which are now being reviewed by medical experts.
Gerrard has been carrying niggling hamstring and groin injuries this season and his latest problem appears to be his ankle.
"Steven was not 100 per cent - you could see that. It was the same for Fernando Torres, you could see that they were a little tired, not as sharp as before," Benitez said.
"But they have been playing well and we felt it was okay to use them both in this game. We need them.
"But credit to Chelsea, they were always controlling Steven and making it difficult for him to play.
"He was not as mobile as normally, Chelsea made it very difficult for him.
"But the difference in this match was that Chelsea played really well and we didn't.
"The injury he had on Saturday was not the problem, his ankle was okay. But we do not know how he is, we will see tomorrow."