Bayern are in Madrid tonight for the first-leg of their quarterfinal tie.
Former Bayern captain Mathaus began by taking a swipe at Vinicius Jr, telling Sky Deutschland: "Vinicius is, of course, a great player, but he's constantly provoking.
"When someone makes a decent tackle on him, he just complains and whines."
The World Cup winner also took aim at Real Madrid's boycotting of the 2024 Ballon d'Or ceremony after Vinicius Jr was beaten by Manchester City midfielder Rodri for the top award.
"Rodri was chosen and they (Real Madrid) said: 'It's unfair. One of ours (Vinicius) should have won. We're boycotting him.' And that's not right. Out of respect for the opponent, the other teams, and the other players," said Matthaus.
He also pointed out that "in a way, you lose sight of the bigger picture. So I don't like how Real Madrid has been in recent year".