Dick Advocaat has warned Sunderland chairman Ellis Short that he will not take the role as the club's manager unless he is given money to invest in the squad.
The Dutchman revealed that he was offered the position beyond the end of the season after guiding the Black Cats to safety in the Premier League.
However, Advocaat has insisted that the club need to invest to ensure that they can push themselves away from the relegation zone next season.
He told reporters: "If they are not clear on the need to invest, then I had better leave. This squad needs five or six good players. It doesn't need quantity, it needs quality. That is what is important, and it is the only way to change things.
"The owner has said that he wants to be challenging for ninth or 10th on a regular basis, and even a little bit higher.
"You have to invest to do that because otherwise you have no chance. You have to invest, and then you can build. Now it starts because it was very difficult for them to do anything when they did not know if they were going to be in the Premier League."
Sunderland play Chelsea on the final day of the season at Stamford Bridge.
