The Foxes boss is also hoping 37-year-old striker will stay and help the club in their attempts to return to the Premiership at the first attempt.
"Les is in Germany at the moment having a series of injections from a specialist that we hope will help his knee," said Adams.
"I have spoken to him and he knows that I want to keep him.
"But he has got to get himself fit first. It is okay agreeing a new contract with him but he has to prove that he will be fit enough to do the year with us."