Costa has been slapped with a four-match ban for spitting at Sassuolo defender Federico Di Francesco, the son of Roma coach Eusebio Di Francesco.
Losi snapped: “These gestures are never done, I think this gesture is unqualified, it is an outrage to human dignity.”
Losi was also asked about Roma captain Daniele de Rossi and the prospect this could be his last season with the club.
He told Soccermagazine.it: “I would be sorry because he is a player-symbol of the team and I would like him to remain in the club.
“De Rossi has shown he loves the team.”