The Brazilian midfielder, who first announced his planned departure back in January, has enjoyed a resurgence under manager Michael Carrick.
His performances have been pivotal, with a series of vital goals helping to stabilise United's campaign during key moments.
Supporters have responded with regular chants of "one more year, one more year, Casemiro", a show of appreciation that has resonated beyond the pitch.
Following a recent victory over Liverpool, the emotional weight of that support was evident, with the chants reportedly moving his wife.
Casemiro has also developed a strong on-field partnership with Kobbie Mainoo, forming an effective and balanced midfield pairing that has been central to United's improved displays.
Speculation over a possible change of heart was fuelled by Matheus Cunha, who hinted that "you never know" and admitted he would like to see Casemiro stay.
However, the midfielder has now firmly dismissed any uncertainty, stating his intention to depart Old Trafford with his dignity intact.
"I don't think there's a chance. There's no chance," Casemiro told ESPN.
"Mostly because of what I said, you know? Go out the big door. I think it was four beautiful, wonderful years and I am eternally grateful not only to the club, but to the fans.
"But I think I have to leave in good terms, I have to go out on top. I will be an eternal United fan here in England and I just have to thank all the love from the fans."
