The 28-year-old had been a doubt after straining his thigh in Wednesday night's 3-1 Champions League defeat to Chelsea.
Related ArticlesLiverpool look to past gloriesPremier League team newsAllardyce: Rafa loves to whingeLiverpool v Chelsea: Man markingDrogba persistence pays offGerrard injury blow for LiverpoolHowever, having undergone scans, the club has announced that Gerrard will be in the squad but it remains unclear whether he will be able to start.
"Steven has some problems with his adductor. He will be in the squad but we still have to decide whether he will start," Benitez told the club's website.
"It is not very serious but we need to analyse the risk for the future as well. We know it's a very important game, so we'll decide tomorrow.
"We have to think about the best for Stevie and the team – both things together.
"This is a very important game, so we know it will be really good if he can play. But if we were to lose him for the next few weeks it could be a big risk.
"I will talk with him and the doctor on Saturday morning before deciding."
Meanwhile, the Spaniard has told his side just how crucial the match is to maintaining a threat on Manchester United.
Having been left shell-shocked by the defeat to Chelsea in midweek, Benitez is urging his players to put disappointment to one side and make sure they are ready for a Blackburn team desperate to haul themselves away from the relegation zone.
"The Blackburn game - that is the first priority now," he said. "Only after that will Chelsea be the priority in the Champions League second leg on Tuesday.
"We will have Javier Mascherano back from now on for both these games and the rest of the season. He is very important to us now.
"We have to believe anything can happen. Firstly we must do the right things against Blackburn and then go to Chelsea with confidence. If we score first there we will be in the game.
"But at Anfield this weekend I know our fans will be behind us again, that is always the case. They will know what the first priority is, and that is to win a league game.
"They know people make mistakes. But they will be determined to help us through this situation.
"To stop the result against Chelsea having a damaging effect on us, we must keep working really hard and prepare properly for the next game."