United suffered their third successive loss in the Premier League, as they went down 1-0 to the Baggies at Old Trafford.
The Red Devils dominated possession, but Chris Brunt's free-kick deflected in off team-mate Jonas Olsson in the 63rd minute and that proved to be the decisive goal in the encounter.
West Brom goalkeeper Boaz Myhill saved Netherlands international striker Robin van Persie's penalty after Saido Berahino's handball offence in the area.
Over the course of the 90 minutes, United had 80% of the possession, took 26 shots of which nine were on target, and earned nine corners.
Gardner, who has returned to his parent club Aston Villa following the end of his loan spell with Forest on Saturday, was following the match and posted the following message on Twitter after full time.
How much do Man Utd miss carrick! What a result for wba well done bro!! Grafter! @CraigGards8— Gary Gardner (@22Gards) May 2, 2015
Michael Carrick missed the game for United against West Brom due to injury, and his absence did have a negative effect on Louis van Gaal's side.
The former West Ham United and Tottenham Hotspur midfielder has sat out the Red Devils’ last three Premier League matches - and they have lost all of them.
Carrick brings a certain vision and calmness to the midfield, and the sooner he returns to action the better for United.