Rafa Benitez admits Liverpool face a nervous wait to discover the extent of Steven Gerrard's injury after the captain limped out of Tuesday's Champions League defeat to Lyon.
The midfielder lasted just 25 minutes of the contest at Anfield due to a suspected reoccurrence of a groin injury, and the boss will now await the results of further tests on Wednesday.
"I think it is the same problem," Benitez told his post-match press conference. "He felt something, so he knew it was better to come off."
Asked if he felt it was a risk playing his skipper, Benitez replied: "It wasn't a risk. He wanted to play, the doctor said he was okay and he has been training for the last two days. Sometimes it is bad luck."
Benitez also confirmed Glen Johnson missed the game due to injury, while youngster Martin Kelly sustained a knock in the second half of our 2-1 reverse.
"We will have to check the players tomorrow," he said. "We have too many problems with different players and we won't know more until we check tomorrow."
The defeat to Lyon leaves Liverpool with three points from their opening three Champions League matches this season.
However, Benitez is confident the Reds can draw on the experience of 2007-08 when his side found themselves in a similar situation and still managed to progress into the last 16 in style.
He said: "It was a difficult game for us, but we were winning 1-0 and had two or three chances that could have changed everything.
"We are really disappointed because it was a difficult game that we could have won.
"But we have done it before and now we have to do the same. We have to be ready for the next game and try to win, and afterwards the same with the other two games in the group.
"We have done it before and we have to have confidence we can do it again."
Manchester United are next up for Liverpool at Anfield on Sunday, and Benitez is confident his players will be ready for the visit of Alex Ferguson's side.
He added: "We will have to prepare the players and push them. We will prepare for the game like always and keep going. It is a question of doing things properly and having confidence.
"Again, I will say we had chances and everything could have been different.
"We have to prepare for the next game. That is our job and we will do it from as soon as I finish this press conference. We have to be ready."