When Dean Collis plays his first game for Cronulla on Monday night, he'll have overcome a cancer scare as well as the knee injury which has kept him out of the Sharks' first two NRL matches.

The former Wests Tiger picked up a medial ligament problem during the pre-season trials but it was something else that had Collis most worried.

"I had a few problems with my ribs, there was a bit of pain there and we found a lump," the 24-year-old told AAP on Thursday.

"I tore something off the bone and that's where the pain was coming from, but on top of that there was a lump."

Collis was sent for extra scans to check on whether he was facing a serious health problem.

"When I first heard it I was a bit scared but the physio here and the doctor kept reassuring me it was nothing to worry about, they were pretty certain it was benign," he said.

"But we went for a few more scans just to make sure and thankfully it all came back good.

"The lump's still there and they said it was nothing to worry about so I didn't really ask any more questions, just as long as I was cleared to play, that was the main thing.

"The lump they said had been there for a while now, it's been there for a couple of years or something.

"The ribs are good."

So is the knee, allowing Collis to start in the centres as a Shark for the first time against South Sydney.

He'll also be starting afresh after managing just 24 appearances for the Tigers in the past two seasons.

"My last two years haven't been great with injury and my form hasn't been up," the former City representative said.

"I think I needed a change, I wasn't happy with the way I was playing.

"I enjoyed my time at the Tigers, I don't have anything against anyone there, I just thought personally I needed something different."

Collis' health wasn't the main concern at the Sharks on Thursday, with backrower Reece Williams recovering in a Sydney hospital following surgery to remove a blood clot from his spine after he collapsed during a NSW Cup game on Saturday.

Williams, who also had an operation to remove a clot from his brain last year after being concussed in an NRL match, was carried off in a game against Shellharbour after making a tackle.

He underwent surgery on Wednesday.

The incident has cast doubts over whether the 2007 City representative will be able to continue his career, with doctors saying the 24-year-old should stay on the sidelines indefinitely.

Sharks coach Ricky Stuart visited Williams on Thursday and said he was in good spirits.

"Reece is a tremendous person and an extremely talented player," Stuart said in a statement.

"Everyone in rugby league wishes him a speedy recovery. Regaining his health is his number one priority and the Sharks will support him all the way."

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