Director of Cricket Steve Rhodes confirmed Joe Clarke is to undergo a scan on the side strain suffered during the warm-up to Worcestershire Rapids NatWest T20 Blast clash with Derbyshire Falcons at the 3aaa County Ground on Friday.
Clarke was forced to pull out of the Lions final two matches in their Tri-Series with Sri Lanka 'A' and Pakistan 'A' because of the setback.
Rhodes believes it is unlikely Clarke will be available for tomorrow's home Royal London One-Day Cup clash with Northamptonshire Steelbacks.
He said: "Joe is desperately trying to get back fit as quick as he can. He's got a little bit of a side strain, we think,which we will know for sure when we've had him scanned.
"He will be trying to get fit for Wednesday but I think that will be a tough call to get back as quick as that.
"The games after that, we are very much optimistic that he can play."
South African paceman Kyle Abbott is again side-lined for tomorrow's game with a foot injury.
Rhodes said: "He is another one who has got an injury and the likelihhod of him playing may well be after the Pakistan game (on July 29-30)."