Jose Mourinho's side lost 2-1 in Spain with Phil Jones' own goal ensuring they passed up a chance to top Champions League Group H.

United, who were already assured of a last-16 place, next face Liverpool in the Premier League on Sunday.

Fletcher said it would be "suicidal" to play an "open game" against them.

Speaking on BBC Radio 5 live, the 34-year-old Stoke midfielder added: "It wasn't a dead rubber because they have Liverpool next and some of the players that played [against Valencia] aren't in the team [regularly].

"There were questions over them. Now it feels like players who should have a point to prove have come back in [and haven't proved themselves] and it's kind of back to square one. It was slow, lethargic, disjointed.

"They are not drilled enough to play Liverpool in an open game.

"It will be instructions to play in Liverpool's half, missing midfield out. You will probably see Nemanja Matic and Marouane Fellaini and pace either side of Romelu Lukaku."

'I didn't learn anything at all'

Jose Mourinho and the Manchester United bench did not look too happy

In Valencia, Marcus Rashford scored a late consolation in answer to Carlos Soler's opener and Jones' own goal.

Defeat means they will play a group winner in the knockout stage, one of Barcelona, Borussia Dortmund, Paris St-Germain, Porto, Real Madrid or Bayern Munich.

Had United finished top, they would have faced either Atletico Madrid, Roma, Schalke, Ajax or Lyon.

Jose Mourinho said he "did not learn anything at all" from the match.

"I think to qualify in this group is a success, never a failure. To finish second in this group is always a success," he added.

"Before the game I told the players if we win and Juve win, we did our job. If we don't win and Juve don't win, we can blame ourselves.

"Apart from a couple of clubs that are clearly much better than the others, I don't think the draw will be significantly different.

"There are teams who finish second that the ones that finish first will not be happy to play against."

'The gap could become a chasm'

United were unbeaten in five games before Wednesday's match, but they sit sixth in the Premier League table, 16 points behind leaders Liverpool and eight points below the Champions League qualification places.

Speaking on BBC Radio 5 live, former Chelsea winger Pat Nevin said defeat at Anfield could see that gap develop into "a chasm" between United and their rivals.

"It's that distance that's been opened up between the top five and everybody else," Nevin said.

"I expected it to be a top six but that gap would look like a chasm if they don't get anything out of the game - [they need] at least a point. It's fingernails stuff.

"Less than that and you are talking about losing the chance of Champions League football for next season this early on and that's a really tough one for Manchester United to take.

"I still think Mourinho will be there until the end of the season, I'm convinced on that. But next season, I wouldn't put quite so much money on it."

Is United's European season over?

Your reaction on #bbcfootball and text on 8111

Jon: I don't think you could get me to watch the game this Sunday if you paid me a million pounds. If Manchester United play like we did tonight, it'll be a cricket score.

Steve: Clear to see that Jose Mourinho went into this game with the mindset that Juve would win and had already settled for second. This club used to strive for nothing but first but not any more. Awful performance.

Jacob: It's actually quite hard to describe just how awful United have been. In truth I should have gave up watching after Phil Jones' coolly incompetent finish, but it has held my gaze like the unfolding of a tragically predictable horror story. I'm unlikely to be so brave when we play Liverpool.

Daniel: That's United's European season over - they've no chance of beating any of the group winners. Glorious chance to win the group tonight with the Juventus result, but Mourinho bottled it even before kick-off with his team selection. Awful.