Everton rejected a bid from United and former manager David Moyes for the England left-back in June.
Speculation has been rife that Moyes will return with an improved offer for Baines, while midfielderMarouane Fellaini has also been linked with a move to Old Trafford.
But Everton manager Martinez told the Liverpool Echo: "Before we went to Austria one club officially contacted ourselves with an offer and it was a final offer.
"They put something over and the valuation wasn't anywhere near the quality of Leighton Baines. That was the end of it but since then there's been all the speculation, which has been part of what the transfer window is.
"There's never been another club or anyone else putting in an offer for Leighton. Since then we've moved on and we're continuing to focus on the start of the season."