The Algeria international was replaced by Christian Maggio after 31 minutes as the Naples outfit were overpowered 4-2 by Pep Guardiola’s men.
And left-back is expected to undergo surgery on Friday, with no date set for his recovery yet.
“I feel fine,” Ghoulam told media.
“I don’t know what went wrong, I had to go off and I only saw a bit of the second half.
“What do I want to say to the Napoli fans? Nothing, I’m sorry for the defeat [on Wednesday].“We have a lot of games to play now, let’s look forward."