Millwall have told Zak Whitbread they want him to sign a contract extension by the end of the month.
The League One outfit are wary of allowing the highly-rated defender to head into next season in the knowledge he could leave for nothing at the end of the campaign when his existing deal expires.
Chairman John Berylson wants to tie the 25-year-old to the Den for at least another year, even if the new contract includes a clause which allows him to leave if the Lions miss out on promotion.
"We are waiting over Zak. July is our deadline on that. We have tried to come up with a contract that would allow Zak to leave if we failed to win promotion," Berylson told the Southwark News.
"I don't want to clip his wings, but he is an important asset to us. We won't give him away, but we would agree that he could move on to further his career."