Gerrard has played just 25 minutes since picking up the problem during England's defeat in the Ukraine three weeks ago.
Related ArticlesFulham v Liverpool: match previewLiverpool fear Gerrard operationMy destiny to manage a big club, says LaszloSport on televisionDirk Kuyt excited by Alberto AquilaniLiverpool in hunt for Juan MataThe Spaniard will also be without defender Glen Johnson after a scan confirmed the £18 million right-back had a small tear in his calf.
Neither player has yet been officially ruled out of Wednesday's meeting with the French side, who won 2-1 at Anfield 10 days ago, but Benitez - already without Albert Riera and sweating over the fitness of virus victim Alberto Aquilani - admits both are doubts for the game.
'Steven got the injury with England and rested for two days and then had the same problem,' said Benitez. 'We treated him and then he could only play 25 minutes [against Lyon].
"He is improving now but we have to be careful. At this moment he is working with the physios and we do not want to take any risks.'
Benitez will, however, be boosted by the presence of both Fernando Torres and Lucas Leiva. The Liverpool manager admitted after the Spanish striker scored in last weekend's 2-0 win over Manchester United that he was only '80 per cent' fit, while he confirmed Lucas has overcome a virus in recent days.
'They have both been training, so they are ready,' he confirmed.
Both Torres and Gerrard have been nominated for the World Player of the Year award, a feat which their manager described as 'very good news' for the club. 'We know they are both world class players,' he added, 'and they both deserve to be there.'