Frizell joined his Blues teammates in camp in Sydney on Sunday but will be carefully monitored over the next week after being knocked out cold in St George Illawarra's loss to Cronulla.

Blues doctor Nathan Gibbs said Frizell was feeling good on Monday and would follow the NRL's concussion protocol before being cleared.

Frizell slumped to the WIN Stadium turf after a nasty head clash with Josh Dugan.

The Blues are taking a cautious approach and on the weekend refused to consider Sydney Roosters half Luke Keary after he suffered his second concussion of the season.

Coach Brad Fittler on Monday added Wests Tigers back-rower Ryan Matterson to their squad as 18th man.

Under the NRL's head knock rules players must be rested for the first 24 to 48 hours after suffering a concussion.

The Blues will train for the first time at the NSWRL Centre of Excellence at Sydney Olympic Park on Tuesday, but Frizell will be eased back in and is likely to wear a no-contact bid for most of the camp.

The NRL's concussion management guidelines say players should only be allowed to return to full contact training after seven to eight days.

Australian Associated Press