Alli's deal with Everton expires at the end of the season.
Thelwell said: "Dele's contract is coming to an end, but our medical team will continue to support him while he completes the intensive rehabilitation program he is currently undergoing following the surgery he had earlier this year.
Advertisement
Advertisement
"Both Sean (Dyche) and I agree that it is important that we ensure Dele's rehabilitation is not affected by his contract situation at such a critical time in his recovery."