Charlton Athletic say they have been unable to agree terms with manager Lee Bowyer over a new contract.
The 42-year-old led the Addicks to the Championship this season with victory in the League One play-off final.
A statement on the club's website said: "Lee has been offered a one-year extension to his contract.
"If Lee does change his mind before his contract expires and chooses to continue his good work at Charlton, he is still welcome to stay."
The club is has been up for sale since 2017, with Cardiff City chairman Mehmet Dalman in talks about a potential takeover.
Charlton's statement added it would not be "good business practice" to offer Bowyer a long-term deal and a big wage increase when the Addicks were losing money and a new owner could be in place in a few weeks.
It continued: "Lee has been offered a one-year extension to his contract at a level which is approximately three times what he had since his last increase when he became permanent manager in September.
"This reflects the strong desire we have to continue to have Lee as our manager. But Lee wanted much more.
"The owner (Roland Duchatelet) understands Lee's point of view, because many Championship clubs pay huge amounts to their manager. It is fair that Lee feels he should be paid like many other Championship managers."
The statement added: "The club hasn't started to look for any other manager in the meantime and does not intend to appoint a permanent manager, since the club is going to be sold.
"A caretaker manager will be announced in due course and in the meantime the other staff members will continue to prepare the upcoming season for which a lot of good work has been performed already."
Bowyer, who began his career as a player at Charlton and also played for Leeds, Newcastle and West Ham, took over at The Valley in 2018, initially on a caretaker basis.
He helped them back to the Championship after a three-season absence with a 2-1 victory over Sunderland at Wembley in May.
When asked about his own future after that win, Bowyer said: "The owner rang me [before the game] to wish us luck and then he said we will speak very soon.
"Whatever will happen with me will happen. I can't control that but I'm sure we will come to an agreement. Well, hopefully."