Manchester United are third in Group A of the Champions League as the second half of the group stage kicks off Wednesday for the struggling side.
They travel to Denmark to face FC Copenhagen in a crucial match, one which former United striker Dimitar Berbatov says the side cannot take lightly despite being the bigger of the two clubs.
"Let's not jump to the conclusion, Manchester United need to take it game by game," Berbatov told Betfair.
"Yes, they're favourites, but what is a favourite anymore? Luton played Liverpool the other day and that was a draw."
"Manchester United need to watch how the smaller teams are playing, to give them respect, otherwise, they will suffer by underestimating them.
"Copenhagen was a tough game last time, let's win against them first and then build up momentum."
The teams last met two weeks ago at Old Trafford in an evenly-matched game that was won on a 72nd-minute Harry Maguire goal. With the scene now shifting to Copenhagen's home stadium, Berbatov urged his former side to do whatever it takes to get the full points because United's final two games of the group stage are potentially even trickier.
"Copenhagen is a must-win game because Galatasaray away is a hard game and Bayern Munich is even harder!" he said.
"If it's going to be a boring, scrappy game, then we must sacrifice to get the three points, no matter what.
"In some games, it's all about the result and not the performance, Copenhagen will be just like this, as was Fulham (last weekend).
"But if Manchester United play the same way they did in the reverse fixture, then there will be problems."