Messi scored his 85th and 86th goals of 2012 on Sunday in the Spanish league, breaking Mueller's 40-year-old record for goals in a calendar year.
Mueller tells Sport1.de "my record stood for 40 years — 85 goals in 60 games — and now the best player in the world has broken it, and I'm delighted for him. He is an incredible player, gigantic."
Mueller scored his goals for Germany and Bayern Munich in 1972. Messi has scored his for Barcelona and Argentina.
Mueller says "he's such a nice and modest professional and I hope he gets one or two more goals in 2012 and that he can then hold onto the record for the next 40 years."