Interim boss Ralf Rangnick says Manchester United must be "sharper in front of goal" after a wasteful display in their 0-0 draw with relegation-threatened Watford.
The Red Devils dropped two more points in their quest for a Champions League place and left the field to boos after being frustrated by the lowly visitors, despite dominating at Old Trafford.
United had 22 shots against Roy Hodgson's side but the only time they found the net, Cristiano Ronaldo was offside.
Ronaldo also hit a post and struck team-mate Anthony Elanga with a goal-bound shot.
Elanga himself failed to provide the finish to a flowing move, while Bruno Fernandes was unable to capitalise on two excellent first-half opportunities.