Benayoun scored the only goal when Liverpool beat Real 1-0 in Madrid in the first leg of the last 16 tie last month, but faces an anxious wait to see if he can play any part at Anfield after colliding with a team mate in training.
Liverpool manager Rafa Benitez told the club's official website on Monday that the player needed a scan to see how serious the injury was.
"Yossi has a hamstring problem and we will know more after the scan," said Benitez, who also has injury doubts about Fernando Torres, Alvaro Arbeloa and Daniel Agger.
"Hopefully he can train today and then we will see. It depends on his reaction after the session and again tomorrow. I think he can be part of the squad and maybe he can play some minutes, but I can't guarantee how much."
Torres has missed Liverpool's last two league matches after twisting an ankle against Real in the first leg and took part in a light training session on Sunday.
