Gallas told GQ magazine: "They are a strong team with lots of experienced players. But, sometimes, they think they're too good. Too arrogant, yes.
"It can make you complacent. We understand that problem. We know we have to score goals, be strong in defence and kill teams in the first half.
"Our squad can win things. And I know that it will be difficult for Manchester United to win."
Nor is Gallas bothered about facing Cristiano Ronaldo.
Remembering his past clashes with the Portuguese wing wizard, he added: "It was not easy against him but it was not that difficult either."