England captain Harry Kane says international team-mate Harry Maguire has been “scapegoated” and faced “unnecessary scrutiny”.
Maguire, 30, has struggled for first-team football and faced criticism after England’s 3-1 away win in Scotland last week, when he scored an own goal.
Forward Kane said Maguire has been “one of England’s best defenders”.
However the centre-back will not feature on Wednesday after being ruled out through injury.
Following the game at Hampden Park, England manager Southgate said the criticism Maguire faced was “a joke” after he was mocked by the home fans when he put the ball into his own net.
Maguire says he “can deal with banter” from fans, but West Ham United striker Michail Antonio says the defender’s humanity is being ignored, while Maguire’s mother, Zoe, said the abuse of her son “goes far beyond football”.
Speaking before Wednesday’s first group-stage match at the Allianz Arena, Kane said: “I think H has come under some unnecessary scrutiny.
“He has probably been scapegoated a bit. He is a really good friend of mine, a great guy and a really hard working professional.
“He has been one of England’s best defenders over recent times and in England’s history.
“It is part of our game now, you are scrutinised all over social media.
“But, knowing him, all he will want to do is work harder, to improve and get better, and stay focused.”
Kane, 30, also warned against complacency when Bayern face United, who have already lost three of their opening five Premier League games.
The striker, who joined the German club from Tottenham in the summer, added: “United have been going through a tough spell recently, but sometimes that can be really dangerous.
“They are looking for a big response and we need to be careful of that.
“We are at home and want to dictate the game, to play the way we want to – but they have some threats as well who we have to be careful of.”