It is understood Friend won't play in Thursday's clash against South Sydney at Allianz Stadium, but there is a fear the injury may rule him out for the remainder of the season.

Friend was struggling to breathe and was coughing in his sleep after his side's win against Melbourne on Saturday night so his girlfriend took him to hospital.

Friend was diagnosed with haemothorax, but the Roosters were unclear about how serious the injury might be.

"We rolled into training for recovery this morning and obviously Friendy wasn't here," skipper Anthony Minichiello said. "He's been in hospital for most of the night with a bit of fluid on his lung so they're working through the process. Hopefully he'll be back recovered and get well soon.

"After the game he didn't look the best. He had a bit of a shoulder knock as well so he was a bit sore and said he was a bit out of breath. But apparently he woke up and couldn't breathe and got a bit dizzy so he took himself to hospital."

The Roosters were unaware of the injury after the match, although Friend's teammates noticed he was struggling in the sheds after the come-from-behind victory.

Minichiello said the injury was a build up of previous knocks rather than one particular incident in the game against Melbourne.

"I think it's been progressive," Minichiello said. "He's had what he thought was a rib injury, and it just kept getting knocked, a few games, he got a knock at training. I think last night was just the last straw. Something happened, so hopefully he can get well soon.

"He's an important part of our team. He controls a lot of what we do through the ruck so hopefully he can come back to training as well as he can and get the body moving. He's very important. He controls the ruck with that hooker play but he also does all that work behind the scenes that no one sees. Everyone loves playing with him."

Friend had been one of the Roosters' best players this season and had only just returned from a separate injury against the Warriors last week.

The Roosters were without Daniel Mortimer after they allowed him to link with the Gold Coast Titans before the June 30 deadline, but back-up hooker Heath L'Estrange was expected to be fit after a knee injury against the Tigers in round 23.

The Roosters had also used utility Mitchell Aubusson in the No.9 role in the past.

Halfback Mitchell Pearce said the injury was no surprise given how little regard Friend had for his body, but recognised just how vital he was to their hopes of going back-to-back.

"He's such a tough bugger and the amount of tackles he gets through in a game, he's going to have a slip up sooner or later," Pearce said.

"We love playing with Nug and hope he recovers quickly ... Obviously to take a player like that out you lose a lot on defence, the amount of work he gets through and the organisation he does there ... Also his short kicking game has improved a lot for us, but, in saying that, Mitch Aubusson has done a really good job filling in.

"He's got that [kicking] option as well. He takes the pressure off the boys with their kicking and he's been putting in some good grubbers recently as well. So he's got that bit of flair about him as well this year, so we certainly need him."