Valencia paid his own tribute to the "super coach" who retires at the end of the season, insisting he is the best in the world - even taking into account the infamous 'hairdryer' moments.
The Ecuador winger, 27, said: "I never thought this moment would arrive. It never seemed real to me that Sir Alex would actually leave.
"It's going to be a very emotional day and the boss will merit every cheer from the fans. We want to dedicate a victory to him on what will be a great day in Old Trafford history.
"What Sir Alex has achieved in 27 years will never be repeated.
"I have been very happy to work for a super coach - the best in the world - and I am tremendously happy to have had the chance to win titles under him. Without him, that wouldn't have been possible.
"And after some grave injuries Sir Alex was decisive in my recovery in that he restored and raised my morale. Privately, he told me how much United needed me and that vote of confidence was the key to my rehab.
"But I shall also always remember his anger in the dressing room after a bad game. He is normally positive but often he'd be critical of us even after victories by two or three goals.
"Against that, he would often appear with a long face and look as though he was lining up an intimate moment - and deceive us with his jokes!
"Today, though, the dressing room is very sad he is leaving. We didn't see this coming but it is fair to say the boss became more serious after we won the Premier League title again.
"It's not just the length of time Sir Alex has been manager or the number of trophies he has won. It's also the way he worked with the players. He is incredible - as I say, the very best. Totally unique."