The trio all started Liverpool's 3-1 win over Lyon on Wednesday in the Reds' final pre-season game.
Per the club's official website, when asked if he will do the same on Sunday, he said:
"I don't know yet in the moment, so that's how it is. We have to see. I don't say 100 per cent not, there's a chance that they will play, yes.
"They will be involved whenever, from the start, maybe we cannot make these changes like today after half an hour or whatever, that's maybe not possible in that game so we have to see.
"We have to see how they react tomorrow, now training is not the highest intensity anymore, now training is about the detail [and] we really need to prepare the game."
The three players only returned to training on Monday after Firmino and Alisson won the Copa America with Brazil and Salah reached the quarter-finals of the Africa Cup of Nations with Egypt.
Firmino went off after half an hour on Wednesday, having netted Liverpool's first goal, while Salah was substituted at half-time.
Goal's Jack Sear was pleased with how the pair performed:
Alisson was withdrawn shortly after the hour mark.
He was responsible for Lyon's Memphis Depay opening the scoring after just three minutes. The goalkeeper failed to deal with a routine cross and conceded a penalty when he fouled Bertrand Traore in his attempt to smother the loose ball (U.S. only):
After the match, Klopp said the incident was comical, but he did not appear concerned about his No. 1.
He told LFC TV (h/t Sky Sports):
"A lot of things were really good, although the first goal we conceded was like slapstick. Welcome back, Alisson!
"He's looked brilliant in training and looked brilliant in the game but it was just one situation—he just needs to get used to his gloves again. Apart from that, it was a good game."
The 26-year-old played a key role in the Reds shipping just 22 Premier League goals last term, and he conceded just once with the Selecao in the Copa America.
Given it was only his first match back following his post-Copa holiday, it's natural he'd be a little rusty.
Beating City in the Community Shield would be a positive start to the campaign, but as it's a trophy of little consequence, Liverpool can afford to use the match as a chance to continue getting their stars up to speed before the important games begin.