Kyle Flanagan says he was surprised to be sin-binned at a crucial point in Canterbury's season-opening NRL loss to Manly, claiming he made minimal contact.

With scores level at 6-6 as halftime loomed, Flanagan was pulled up by the bunker for putting a hand on the back of Tom Trbojevic as the Manly fullback chased a kick and fell to the ground.

The contact appeared to have come after Trbojevic pulled up when he realised he had overrun the play, before Flanagan put his hands onto the back of the Manly star.

Canterbury conceded two tries while Flanagan was off the field - albeit with one from an error from a loose ball - and were never really back in the contest before losing 31-6.

"I was definitely quite disappointed about the call," Flanagan told AAP.

"I won't elaborate on it too much, but I thought it was minimal contact.

"Definitely surprised, spending 10 minutes off the field. It's not the result we wanted."

Flanagan had earlier been solid in defence across several Manly assaults on the line, in a match where his father Shane sat in the Sea Eagles' coaching box as an assistant.

Canterbury coach Cameron Ciraldo did not blame the decision on the result in his first game in charge, and said his players had to learn to handle adverse situations.

"I only saw it on the little screen, but I didn't think he was going to go to the sin-bin," Ciraldo said.

"It was disappointing for us but I thought we could have handed it better when he was off."

The Bulldogs desperately missed their injured middle forwards as Manly rolled through a pack without Tevita Pangai, Luke Thompson and Chris Patolo.

With eight new players, the Bulldogs completed at 68 per cent, kicked the ball out on the full three times and had the impact of Viliame Kikau dented by the defensive workload.

Reed Mahoney was the main positive in his first game for the club with one try and 52 tackles.

There were also questions again about the independent doctor's decision to stop play and order Jacob Kiraz off the field late in the first half with Canterbury on the attack.

Kiraz looked confused by the order, a day after Kalyn Ponga expressed similar concerns in Newcastle's loss to Warriors.

"I didn't see him get a knock but obviously someone picked it up," Ciraldo said.

"We were in a good spot there, had them on their line and we were looking pretty good.

"I didn't see the incident but he was clearly fine. It made things harder for us."