Matthaus remains unconvinced by former Liverpool winger Luis Diaz and also believes they lack cover for prime centre-forward Harry Kane.
He told BILD: "The arrival of Luis Díaz, a 28-year-old Liverpool wanted to sell because he wasn't renewing his contract, for €75 million isn't really that great.
"The Colombian certainly has speed and quality, so he'll do well and can replace Leroy Sané, but if the club were honest with themselves, they'd have to admit he certainly wasn't a first-choice option. After Nico Williams, Rafael Leao, and Jamie Gittens, Luis Díaz was actually only number four on the list of targets. And I don't see any real replacement for Harry Kane; he's a risk."
Regarding any Bundesliga title threat, however, Matthaus has little doubt: "Only Borussia Dortmund is a credible rival. If Bayern doesn't complicate their own life with problems within the club and the team, BVB won't pose a threat either.
"The assessment of Bayern's season will depend above all on their Champions League campaign."