Asked if he is fully behind Mourinho, Valencia replied: "One hundred per cent".
Mourinho has come under increasing pressure in recent weeks because of the results and was involved in an apparent training-ground dispute with midfielder Paul Pogba last week.
Manchester United are a club with proud traditions.
"I am not pleased, of course, with the result which is not a good result but it is not a bad result". "The decision [about the captaincy] is for the coach to make, now we need to see the positives".
Valencia added: "What I can say from the inside is that the lads are calm, working every day with a good attitude".
Saturday will see United host lowly Newcastle United before the global break and left-back Luke Shaw is desperate to return to winning ways.
Manchester United extend winless run in dour stalemate with Valencia
United have one more home match before the global break, with Newcastle United visiting Old Trafford in the Premier League on Sunday.
"We have Newcastle before the league stops (for the worldwide break) then we have Chelsea and Juventus in three days. It's hard", Shaw told MUTV . "I think his mouth is out of control and he's embarrassing the club".
"We had probably a couple of the biggest chances to win it but I have accepted the result as a fair result".
"From the Lowry Hotel we took 75 minutes". We should be winning these games.
Having been held at home by Wolves, knocked out of the Carabao Cup by second-tier Derby and humbled at West Ham, their winless run stretched to a fourth match as attention switched to the Champions League. Four points is okay I guess but we should have six.
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