Fans of Inter poked fun at the the Swedish international by doctoring the image taken from the front cover of his recently released autobiography.
Instead of the title ”I am Zlatan Ibrahimovic", the sign read, in all capital Swedish letters, ”I'm a Gypsy" ('Jag är en zigenare').
It is not the first time the Swedsih striker has been singled out for specific abuse by rival fans.
Similar jibes have been a regular feature in the big clashes with Milan's greatest rivals Juventus and especially during local derbies against Inter at the stadium which is shared by the two teams.
Zlatan though, was keen to play down the incident after the game, which Inter won 1-0.
”I don't care about it, its not something that worries me” he told the Aftonbladet newspaper after the game.
”It was fun for them today, they get three points, we lose. That is how football is.” he added.
It was a bad day for the Swede, who failed to make an impression during the game which was decided by a single goal from Inter's Diego Milito.
The Loss not only ended Milan's 12 match unbeaten run but also saw them surrender their lead at the top of Serie A.
The banner mocking Ibrahimovic is the latest in a long line of racist incidents at football matches in the top flight in Italy.
The Italian league has long struggled with the problems which have led to some games being temporarily halted and teams playing European competitions being reported for the behaviour of fans towards black opposition players in particular.
No official complaints were reported after Sunday's game however.