The Dubs are now guaranteed a semi-final spot but O'Sullivan was a cause for some concern for manager Jim Gavin.
"The indications at the moment are that it's not too serious. He came off as a precaution," Gavin said.
However, Gavin noted O'Sullivan's long-standing hamstring trouble and suggested the player could be rested for a large chunk of the coming weeks.
"Cian has a history of those sort of injuries," Gavin said. "He'll be assessed by the medical team over the next few days."
Asked whether he would be fit in time for the start of Dublin's League campaign, Gavin replied: "It wouldn't be the priority, to be honest. If he can make an appearance in the National League, I'll be happy."
The was better news on Michael Darragh Macauley, who was withdrawn from last Sunday's win in Carlow but may, according to Gavin, play some part on Sunday in Parnell Park when Wicklow come to play the final match in the group.
"There is lots of fatigue there," commented Gavin of the levels of wear and tear within the group.
"You want to put your best foot forward so it's a challenge in that respect. We will take a close look on Sunday to see what guys are fatigued.
"The guys will let us know how they're feeling tomorrow and we will assess it. We'll give them a few days off. "
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