The 26-year-old was signed for £27.5 million from Everton last September but back and wrist injuries restricted him to just 16 Premier League appearances last season.
Fellaini has been linked with a move away from United this summer following the arrival of new manager Louis van Gaal.
And when asked by Sky Sports News if he will be at Old Trafford next season, the midfielder replied: "We will see after the World Cup."
Fellaini has appeared in all four of Belgium’s World Cup fixtures and netted the equaliser in his nation’s opening 2-1 win over Algeria in the group stage.
When asked if he had proved a point with his displays for Belgium, Fellaini said: I don't have to prove [anything] - I've been a professional footballer for eight years.”