The Germany international, who had only just returned from injury, is facing up to three weeks on the sidelines with medial ligament damage
The Germany international suffered a knee injury in Sunday's 1-0 win at Napoli and, although it has not yet been established how long the striker will be out of action for, he will play no part in the midweek meeting with the Rossoneri at the Artemio Franchi or Sunday's trip to Sampdoria.
"Fiorentina announces that the athlete Mario Gomez today [Monday] underwent an orthopaedic examination and diagnostic tests following the reported sprain in his left knee during yesterday's league match," a statement on the Viola's official website read.
"They have detected first-degree collateral damage of the medial ligament.
"The athlete must observe a week of rest and the appropriate treatment before undergoing another clinical and radiological examination."
Gomez had only returned to action last month, after five months on the sidelines with a knee injury. It has been reported that this latest setback could rule him out for at least three weeks in total.