Fittler tore his rotator cuff in a Tony Puletua back-slam against Penrith three weeks ago and lasted just five minutes of the Roosters' win over South Sydney before copping a heavy knock on the shoulder and taking an early shower.
"I was going through some discomfort - little things like passing the ball and things like that," Fittler told Channel 10.
"I think it's important for me and my shoulder to have a rest at this time of the year.
"If I kept going then I would have been just a passenger in the semi-finals.
"So given the win yesterday, it gives me a good chance to have a couple of weeks off."
Fittler, 31, will visit a specialist on Wednesday and continue to undergo intense physiotherapy before declaring his availability again.
But there is some chance the former Test five-eighth might also sit out the premiers' grand final re-match against the New Zealand Warriors in round 25, also at Aussie Stadium.
However, Roosters football manager Brian Canavan stressed Fittler's injury was not a long-term concern, despite Fittler admitting he may need surgery at the end of the season.
"There is the possibility of an arthroscope at the end of the year, but he doesn't need one now," Canavan said.
"He could have one, but its not necessary".
"So it (the injury) is not major."
Roosters coach Ricky Stuart hasn't completely given up hope of having his skipper on deck against Manly.
"Ricky said this afternoon that if he scrubs up tomorrow at training, he might name him on the off chance that he can play," Canavan said.