The State of Origin forward is in isolation and is awaiting the results of a COVID-19 test after he invited an unregistered guest to his room overnight.

From midnight, Melbourne players and staff were free of strict quarantine "bubble" conditions, given it had been two weeks since they'd played a team from NSW.

However it's believed the woman, who was stopped by police as she departed, had arrived before that deadline while she wasn't on registered guest list.

Welch apologised for his actions, which meant he was unable to train Friday or play in Saturday night's clash at Sunshine Coast Stadium, leaving coach Craig Bellamy livid.

He was due to return after a one-match suspension for a crusher tackle with Tino Faasuamaleaui set to take his place in the line-up and Max King likely to come on to the bench.

"I'm incredibly remorseful and sorry for my actions," Welch said in a statement.

"I love this game and everything it has given me and I'm shattered that I have let everyone down.

"Calling my parents to let them know about this was the worst phone call I've ever made.

"I know it's a privilege to play in the NRL and I want to apologise to all for any damage I have caused."

The Storm briefed the NRL Integrity Unit and Queensland Government early on Friday once notified of the breach, which is their first since relocating from Melbourne to the Sunshine Coast in July.

Chief executive Dave Donaghy wouldn't reveal the player as Welch during a Friday morning press conference but said the player was "incredibly upset" while the club was also very disappointed in his actions.

"There was a possible breach late last night with an unregistered guest to the bubble's premises," Donaghy said on Friday.

"We disclosed the matter to the NRL early this morning ... we are seeking some further details."

He said he spoke to Queensland's Chief Health Officer Dr Jeannette Young on Friday who assured him there was very low risk of COVID-19 transmission among the community.

The club expects the results of Welch's test in 24 hours.

"We're confident the test won't come back anything other than negative but it has to go through a process," Donaghy said.

Storm and Welch will now await the findings of the NRL Integrity Unit, with the 26-year-old facing a potential fine

The incident isn't likely to affect plans for Melbourne to re-sign the popular clubman, who recently knocked back an offer from St George Illawarra.

Australian Associated Press