David de Gea believes a lack of quality is costing Manchester United this season.
Ole Gunnar Solskjaer's side suffered a 2-1 defeat by Astana in the Europa League on Thursday.
They have also struggled in the Premier League and are already nine points adrift of the top four after 13 matches.
"The team is what it is, and results are what they have been recently," De Gea told Sky Sports. "It's true that the first half [at Bramall Lane] was horrible, probably one of the worst this year.
The reaction of the team in the second half was important, but it's not enough. We should win these type of games to be on top, we need to win four or five games in a row to be at the top, but at the moment the team is not playing so well.
"We're giving it everything, we're trying to get those big wins that can put us high up in the table, but the truth is at the moment we're not consistent enough, there's much to train and much to improve.
"I don't think it's through any lack of effort, the boys are leaving everything out on the field in training and games. You could point maybe to a lack of quality in certain areas, but certainly not a lack of fight."
De Gea committed his future to United earlier this season, putting pen to paper on a new four-year deal.
And the Spaniard says he feels settled in Manchester and is pleased to have his future resolved.
"The truth is I feel like at home here," he added. "There are times when I am in Spain and I'm really looking forward to coming back here, at home in Manchester.
We've been here for a lot of years and I feel like people appreciate me here, I've made a lot of friends and I'm thrilled to be part of this club.
"It's been a long time that I've been playing here and it's not an easy thing to keep playing at the highest level and to maintain that level.
"I personally hope that we can get more accolades in years to come by working hard and playing to that same high level.”
United return to Premier League action when Aston Villa travel to Old Trafford on Sunday.
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