United welcome the struggling Hammers to Old Trafford for the first of two meetings in four days on Sunday.
Slaven Bilic's side come here in the cup on Wednesday in a welcome distraction from their disappointing league campaign so far in which they currently reside just outside the bottom three only on goal difference.
That's a far cry from their success of 2015/16 when they beat us in their last ever match at Upton Park - one of four meetings last year - on their way to an impressive seventh placed finish in the Croatian's final season in charge.
United, buoyed by Thursday's impressive 4-0 win over Feyenoord, have Zlatan Ibrahimovic back after his one-match suspension against Arsenal.
Wayne Rooney, on what could be a record-breaking day for the skipper, and Henrikh Mkhitaryan look set to retain their places after impressing in that European tie, but Chris Smalling and Eric Bailly remain sidelined with Marouane Fellaini doubtful again.
There are no new injury problems for Mourinho and United.
Captain Mark Noble is available for the visitors after a ban, but Winston Reid is out after his red card against Tottenham.
Pedro Obiang is expected to be fit despite an ankle problem.
Mourinho believes the visitors are in a false position, and said:
"The players have to fight to win their positions, they are all friends and colleagues so there is a good spirit but I can only play with 18 players, not 19 or 20.
"Against Stoke and Burnley the opposition goalkeeper was man of the match so we have to be scoring our chances, and need to be clinical.
"We play another difficult and important game on Sunday so let's see if we can get points - big results are not usual in the Premier League but it can happen.
"There is a great balance between the teams and every game is difficult, we need to four or five matches in a row so that is what we will try to do."
"We play them also on Wednesday in the cup but for now focus is on the league and this game.
"It is a very competitive league with a lot of quality and things can change very quickly, we're a bit of a distance away but the team is in good shape and we have been playing well."
Rooney goes into this match on the verge of history.
He needs one goal to equal Sir Bobby Charlton's club-record haul of 249 and two to surpass it and become the all time top goalscorer for both United and England (not bad for a player supposedly past it).
Form guide: United W D L W D W West Ham W W W L D L
Match odds: United 5/4 Draw 7/2 West Ham 6/1
Referee: Jon Moss