United travel to Transylvania, the supposedly vampire-filled setting of Bram Stoker's Dracula, for their second Group H fixture on the back of a disappointing 3-2 home defeat against Tottenham on Saturday that left them four points behind Premier League leaders Chelsea.
It was United's first loss to Spurs at Old Trafford for 23 years and their first Premier League defeat against the north London club in 23 meetings, but far more concerning was the sloppy manner of the defending by Alex Ferguson's side.
Not for the first time this season, United's lack of pace at the back proved fatal, with Gareth Bale repeatedly exposing the ageing Rio Ferdinand.
Of their six matches so far, United have been behind in five, while they have kept just one clean sheet and conceded nine goals, leading French left-back Evra to fear his team could suffer even greater embarrassment against Cluj unless they show more mental strength.
"The game is 90 minutes long and we deserved to lose because we only played for 45. To concede three goals at Old Trafford is not good enough," Evra said.
"The problem is in our heads. It looked like we stayed in the hotel. The first 45 minutes had no speed, no focus, we didn't win a lot of challenges and we conceded some silly goals.
"Maybe I am hard with myself and the team but we only showed the United face in the second half.
"We still have a lot to do, but we have to forget that first half against Spurs.
"I hope it was just an accident and we can get back the winning mentality that we showed in the second half in our first Champions League game against Galatasaray."
On paper United's encounter with the Romanian champions looks exactly the kind of undemanding fixture that should allow Ferguson's side to restore their equilibrium with a morale-boosting win.
But United were knocked out at the group stage of the Champions League last season after underestimating supposedly inferior opponents.
Cluj shocked Portuguese side Braga with a 2-0 win in their opening group fixture and Ferguson has shown them respect by revealing he is unlikely to rest too many key players.
"There's no chance I'll be going with kids in this one. We will play the experienced players," he said.
"Cluj knocked out Basle over two legs in the qualifier -- that shows where they are.
"To win in Braga takes some doing. It's not an easy place to go. We are taking it seriously. They think they can qualify now."
Although United were unconvincing in that 1-0 win over Galatasaray at Old Trafford two weeks ago, a similar result on Tuesday would put them firmly on course for the last 16.
However, Ferguson has a defensive injury crisis after Northern Ireland centre-back Jonny Evans hobbled off the pitch with a dead leg at full-time on Saturday.
Ferguson hopes Evans will recover in time for the Cluj clash, but if he doesn't young defender Scott Wootton could make his European debut as Nemanja Vidic, Chris Smalling and Phil Jones are already sidelined.
United goalkeeper Anders Lindegaard has no doubts Wootton would be up to the challenge after seeing him in action in the reserves.
"I'm a big fan of Scotty's," he said. "I've played a lot of games with him. He is a no-nonsense player with a real calmness to his game."