Avram Grant claims Lens are jeopardising their chances of selling Aruna Dindane by denying the player game time.
The Portsmouth boss is angered at the situation facing the Ivory Coast international as he would be a welcome addition to his first-team plans at present.
However, he is unable to pick the striker, who is on a season-long loan, as one more appearance will trigger a clause in his contract stipulating that Pompey must pay Lens £4million.
Portsmouth, who slipped into administration in February, cannot afford such a payment and as such are forced to leave the player in limbo.
A few clubs, including Blackburn, have begun to sniff around the Africa ace with the intention of launching a summer raid.
However, a lack of action may force them to turn their attention elsewhere, to the detriment of the player and his parent club.
Grant cannot understand why Lens steadfastly refuse to relax their stance and do not allow the 29-year-old to see out the 2009/10 campaign with regular football.
"I don't know what is happening with Dindane at the moment because I'm not dealing with Lens directly," said the Israeli following the 2-1 defeat by Aston Villa on Sunday.
"I have said it before and I will say it again though, they need to resolve it.
"If they want to sell Dindane then they will make it easier by allowing him to reproduce the kind of performance that he showed in the (FA Cup) semi-final against Spurs. I don't understand it but this is their problem.
"A contract is a contract but I don't understand why they are doing this."
Skysports.com reported on Monday that Dindane is set to return to France in an effort to thrash out a deal with Lens.
He is desperate to play again before the season is out, especially in the FA Cup final, and is hoping a truce can be reached.