Ole Gunnar Solskjaer lamented his side's inability to put the ball in the net after they suffered their seventh defeat in nine matches.
United were well beaten by Manchester City at Old Trafford as goals from Bernardo Silva and Leroy Sane gave the Blues a 2-0 victory.
The Red Devils are now goalless in their last three outings, shipping nine at the other end in the process, in defeats to Barcelona , Everton and City.
And Solskjaer bemoaned the lack of clinical edge his side have shown in the last week.
"I've not reflected on the statistics but I've reflected on we don't score goals," Solskjaer said. "Make efforts, we created chances today but we don't take them.
"And of course that's something we need to improve on, something you can't really say is a lack of effort but the quality in the end today wasn't good enough today either."
United are now facing an uphill battle to reach the top four and qualify for next season's Champions League.
They sit three points adrift fourth-placed Chelsea with just three games remaining.
Arsenal are a point back from the Blues having lost at Wolves on Wednesday night, while Tottenham's win over Brighton on Tuesday means they now have a four-point cushion to fifth place.
City, meanwhile, have leapfrogged Liverpool to move back to the top of the Premier League.
They are a point clear of the Reds with three games left and go to Burnley on Sunday.
