The Portuguese powerhouse will face off against the Red Devils in their next Europa League showdown.
With Manchester United's poor performance this season, the pressure is mounting on them, but Bruno is not taking them lightly.
“I've heard a lot of people saying that he (Ten Hag) was coming with a rope around his neck, but it would be a huge mistake (to underestimate United),” said Bruno to reporters.
“We are talking about world-class players. If you tell a different story, it doesn't relate to the truth.
“Any club has problems, but we have to be on our toes and very alert.