Tony Watt will be assessed by the club's medical team later today after coming off early in Saturday's match with Preston North End.
The Scottish international pulled up just five minutes into the match at Ewood Park, immediately signalling to the bench that he was unable to continue.
"We think it is his groin, so we'll have to wait and see how that is," Lambert told Radio Rovers.
"We'll see how he is on Sunday, but when somebody comes off with a groin problem it can actually be worse than what you think.
"But we'll have to see how he is."
