Queensland's smooth State of Origin build-up has hit a hurdle just hours before Wednesday night's kick off with several players being treated for a stomach virus which swept through the Maroons camp overnight.

Team doctor Roy Saunders said several players, including forwards Nate Myles and Dallas Johnson, had been vomiting and suffering from diarrhoea.

Skipper Darren Lockyer is believed to be one of the players under treatment but Saunders declined to name the other ill players.

At this stage the Maroons have no plans to rush in any back-up players but that could change later in the day if their conditions worsen.

However Queensland's 18th man Neville Costigan has been in camp with the Maroons all week and the hard-hitting Dragons forward can slot into the side if required.

Dr Saunders said the main concern was that the players would be severely dehydrated because of their vomiting and diarrhoea.

Myles and Johnson were the first confirmed sick players on Tuesday night.

"The situation is that we have a number of players who have had upset tummies, vomiting and diarrhoea who are not well enough at the moment," said Dr Saunders before the players traditional team walk through the streets of Parramatta.

"It's an evolving situation. We'll monitor them during the day, see how they go and then make some decisions later on this afternoon.

"It will all depend on how well they pull up.

"I'm monitoring them and trying to keep their hydration levels up and trying to keep the symptoms at bay."

Dr Saunders said "hopefully" they would all be fit to play.

"We have to give some of the players anti-medications to control the vomiting and diarrhoea," he said.

All the players, including those affected by the virus, took part in the 15-minute team walk where they were heckled and cheered and even had a few photos taken.

Myles was bed-ridden on Tuesday and missed Queensland's final training run at ANZ Stadium.

"He's up and about, but up and about is different from being able to play Origin," Dr Saunders said on Wednesday.

Brought to you by AAP © 2024 AAP