The 29-year-old arrived on Thursday morning at the club's Melwood training complex for fitness tests which were reviewed by Liverpool's medical team before it was decided he needed a scan.
The England midfielder struggled with the injury during Wednesday night's 3-1 first-leg defeat by Chelsea, when he was man-marked by Michael Essien.
Gerrard was sidelined in February with a hamstring injury sustained in the FA Cup trilogy with Everton, and he has also suffered previous groin problems this term.
Before the Chelsea defeat there had been fears Gerrard was still struggling from the ankle injury that forced his precautionary exit from Saturday's win at Fulham. But Gerrard trained with the squad on Monday and Tuesday, and was passed fit to play.
But now Liverpool are bracing themselves for Gerrard missing Saturday's home Premier League game with Blackburn as well as the quarter-final second leg at Stamford Bridge next Tuesday.
Liverpool manager Rafael Benitez was concerned about his captain's fitness after the Blues match. He said after the game: "Steven was not 100%, 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. "But they have been playing well and we felt it was okay to use them both in this game. We need them.
