The Scotland international, who has been in prolific scoring form this season, was linked to West Ham United.
While a bid was launched for McTominay and teammate Harry Maguire, United did not accept the offer.
Speaking to reporters on Monday, McTominay stated: “There is always speculation. It was always a case of work hard.
“Faith in me from the manager has been massive and you want to repay that as much as you can.
“In the life of a footballer you will always have ups and downs - it is not always sunshine and rainbows.
“I have had an opportunity and want to do what I can to support the team."