The Belgium global has been receiving treatment for an ankle injury at the Move to Cure clinic in Antwerp, missing the last three games including the team's 1-0 Premier League season-ending win over Watford at Old Trafford on Sunday.
It is the highest league position since Alex Ferguson stepped down five years ago and fans showed their affection for their former manager by singing how much they loved him on a sunny Mancunian afternoon.
Carrick will join José Mourinho's coaching staff, the Portuguese indicating he will one day be his new No 2, following Rui Faria's departure in the summer.
There was talk that Mourinho might give a couple of United's youngsters a chance to shine on the big stage but this was not the case. I've made lots of changes in the team not because of that.
United started the game poorly, making a number of sloppy errors which the Hornets perhaps could have done better with. "Why always Lukaku? Why always this player?' 'That guy doesn't have a chance to start, the other one is on the bench".
Man United later confirmed that the 22-year-old is injured, with his cousin taking to Twitter to claim the winger has a little bit of discomfort in his leg.
Marcos Rojo nearly presented Watford with a golden chance to level 20 minutes from time when Will Hughes blocked a lazy pass from the Argentine, but the offside flag was raised when Gray made a movement towards goal. Firstly, Sergio Romero kept out a point-blank header from Richarlison as he tipped the ball around the post. Gerard Deulofeu also fired a shot straight at the United goalkeeper.
It took United a while to get going, but they did create a number of opportunities following the restart.
Carrick left the field to a well deserved standing ovation after 83 minutes, replaced by Paul Pogba, plus hugs from his teammates and manager. It was his 464th - and in all likelihood, barring a spate of injuries in the coming week - last appearance for United.