The Brazilian's usual spot in attack alongside Sadio Mane and Mohamed Salah has come under scrutiny like never before due to the form of Diogo Jota, whose hat-trick at Atalanta on Tuesday took his recent form to six goals in his four matches.
"Jota scored a hat-trick, but that doesn't mean he automatically goes into the team against Man City," Barnes told talkSPORT.
"I think who plays depends on what the games are and who they're against and how that team plays.
"Against Man City, where you're not going to have as much possession, maybe Firmino will be a better bet. You need a player like Bobby Firmino to not only get hold of the ball but also do his defensive work.
"If you're playing a game against Atalanta or Leeds, a more open team, they you can see Jota coming in."