The Germany legend has followed the lead of Uli Hoeness in condemning the Sweden striker for his outspoken comments.
The Paris Saint-Germain striker played under the current Bayern coach during his time in charge of the Blaugrana but fell out of favor at Camp Nou and left to join Inter in 2011.
After Bayern president Uli Hoeness labeled Ibrahimovic a 'prima donna' for calling Guardiola a 'coward' in his autobiography, Rummenigge followed suit in hitting out at the 31-year-old.
"I would recommend to him to keep a sense of proportion. He's been previously convicted by UEFA," he said, referring to the ban Ibrahimovic was handed during last season's Champions League.
"That's gross unsportsmanlike behavior. I would not do that if I were him, otherwise UEFA might consider this case. But maybe stupidity is part of developing your character."
Both PSG and Bayern are in Champions League action Wednesday night against Benfica and Manchester City respectively.