Injuries to Origin hopefuls Ben Hunt, Jack de Belin and Tariq Sims added to St George Illawarra's woes as they surrendered top spot on the ladder in a 28-2 loss to the Panthers.
The Dragons were held tryless for the first time since round 14 last year as their attacking mojo deserted them and the injuries to Hunt (corked thigh), Tariq Sims (leg) and de Belin (hip) only made matters worse.
With the NSW and Queensland sides to be chosen on Monday, McGregor remained upbeat for his star trio, suggesting they should be right to play in Game One if chosen for their respective states.
"Ben got a bump in the leg and Tariq got a knock as well. They were affected but they won't be in any doubt for Origin selection or when we play next," McGregor said.
"Jack aggravated an old injury but I'd say he'd be OK too."
McGregor said Hunt was determined to stay out on the field but the Dragons medical staff decided to take no chances with their star halfback.
Match Highlights: Panthers v Dragons - Round 12, 2018
"He was limping around and he wouldn't have been as effective as he needed to be [if we'd left him out there]," McGregor said.
"It's got to be about the welfare of the players in that situation, not just winning a game of footy."
The Dragons have now lost two of their past three matches and share a 9-3 record with the Panthers.
Both sides have a bye in round 13.
"We would have liked to play better going into a bye, there's no doubt about that. We knew how important this game was," McGregor said.
"The second half they were much more dominant, their line speed was good and they were more physical than us.
"They dominated field position, the halves played over the advantage line, engaged the line well and they were just too good on the night."
Hunt will be fine: Aitken