The Scotland Under-21 player was on loan at this season Lierse and his performances have also led to interest from Standard Liege and Zulte-Waregem.
Watt scored nine goals in 17 matches for Lierse, although he was banned from playing during the past two months after manager Stanley Menzo in two separate interviews. His future at Celtic is still unclear.
"Tony Watt is still an option," said Luc Devroe, the Oostende techinal director. "We, like other clubs, have talked with him. Celtic are still to decide whether they will sell him."