The Belgium international is expected to sign a new two-year deal at Old Trafford.
Fellaini attracted interest from AC Milan, with Arsenal having held talks with him last month.
But now, speaking ahead of the England game on Thursday, he has revealed he’s made his decision.
“I know where I’m going to play next year and that does not affect my performance at World Cup,” Fellaini said on Tuesday.
“The contract has been signed and I’m going to announce it within a few days.”
Asked whether the uncertainty over his situation had affected him mentally.
He said: "No, since a few months, I am used to it. I am strong mentally to deal with it and soon I will say where I will be playing next season."
The player added that an official announcement will be made on July 1.