The goalkeeper, already linked with a move, has cast his future further into doubt following an admission from his agent that he is unlikely to sign a new deal with the club
The Belgian still has two years remaining on his deal with the Black Cats and shone in all 38 of the club's Premier League fixtures last season, prompting speculation of interest from other Premier League clubs.
And Mignolet's agent, Nico Vaesen, has hinted that a move in the near future could be in the offing, with teams courting the player already.
"I think it is very unlikely that he will sign a new contract," Nico Vaesen told the Sunderland Echo.
"Simon has obviously come to a point where he wants to step up a level and there is a lot of interest in him. He is very ambitious and wants to play in the World Cup, in Brazil, next year.
"It was a good thing that Sunderland stayed up and it is a fantastic club where he has had three great years. But it is maybe time to step up a level and play for a club competing for a European spot."
Insisting that the ultimate decision is up to Sunderland, he added: "All teams that are interested in Simon, we direct them to Sunderland.
"He still has a two-year contract there and any interested clubs have to agree a price with Sunderland first. That is the way we conduct our business."