David de Gea issued a damning assessment of Manchester United's quality and acknowledged it will be "very difficult" for them to finish in the top four.
United succumbed to a surprise 1-0 loss to relegation-threatened Everton at Goodison Park on Saturday, with Anthony Gordon's deflected strike proving to be the difference.
Ralf Rangnick has now triumphed in just eight of his first 17 Premier League games as the Red Devils' boss, giving him a win percentage of 47% – the worst of any manager the club has had in the competition.
It was United's eighth defeat of the season – only the eighth time they have lost that many games in a single campaign but the sixth since 2012-13.
They could find themselves six points adrift of the top four by the end of the weekend, with De Gea admitting they lack the requisite quality to qualify for next season's Champions League.
"We knew before today they were struggling and how difficult it was going to be," De Gea told BT Sport.
"We don't score, we don't even create proper chances to score. I don't know what to say, to be honest. We're not good enough, that's for sure. It's going to be very difficult now to be in the top four.
"Of course, it's not the perfect atmosphere. They were tired, they were nervous, but they keep going and keep fighting. They had more desire than us, which is not acceptable. It's very sad to lose today."
Rangnick will move into a consulting role at Old Trafford at the conclusion of the season, with Ajax boss Erik ten Hag reported to be the frontrunner to take over.
Mauricio Pochettino has also been linked with the role, but Rangnick does not believe the uncertainty can be used to excuse a dismal run of one win in seven in all competitions.
"I don't think this should be an excuse. We are Manchester United. We have lots of international players. There shouldn't be an alibi," Rangnick said.
"There will be a new manager next season. If this is announced now or in 10 days, it shouldn't have an impact."
He added: "If you don't score a single goal in 95 minutes, we have to be disappointed. We had a good start and should have created more chances out of that domination. Then we concede a deflected shot and lost a bit of our composure.
"The second half we were trying to add creativity with substitutions, but we didn't always take the right decision.
"We had to do something. We needed a goal and we decided to bring on [Juan] Mata and more verticality with [Anthony] Elanga.
"They were defending with their players in the last 35 minutes. We didn't find the right player at the right moment. We didn't have enough players in the box when we played crosses."