St George Illawarra have called on the NRL to reassess the concussion guidelines after they were forced to play the last 88 seconds of the match against Melbourne with 12 players.

The Dragons played the final minute-and-a-half a man down when Dan Hunt was taken from the field as a result of Joel Thompson's concussion.

Thompson was taken from the field in the 66th minute, and under the new concussion rules, the Dragons were allowed a free interchange to assess his condition.

The Dragons then had 15 minutes to get him back on the field, otherwise the Thompson interchange for Will Matthews would count as one of their 10 replacements.

There was less than 15 minutes remaining on the game clock when Thompson left the field, but two minutes and 26 seconds of stoppages for a video replay and scrums meant the Dragons would rue their decision to use up their last interchange.

With 88 seconds remaining, and Melbourne trailing by just two points, the 15 minutes elapsed, forcing the Dragons to take a player, which happened to be Dan Hunt, from the field with the game in the balance.

The Dragons are still seething about having lost the match after the siren, particularly when the try was scored on the same side of the field where Thompson would have been defending.

St George Illawarra and New Zealand Test winger Jason Nightingale took aim at the NRL guidelines, furious the club was punished for looking after the welfare of one of its players.

"We'd used all our interchanges and were relying on Joel Thompson to be OK, but his health wasn't OK and we got punished for that," Nightingale said.

"I don't like that we've been punished for doing the right thing by our player. There have been plenty of examples where people have been in the grey area on whether they should continue and 90 per cent of them have gone back on. It's a shame that we've been punished for doing the right thing by our player.

"Joel wasn't right to go back on – we could have put him back on like a zombie, but it wouldn't have been good for his health, which is the most important thing. It's a shame we were punished for that, especially because we were awesome in that match and didn't deserve to lose that game."

Thompson, who was playing at right centre after Dylan Farrell left the paddock in the first half with a pectoral injury, was then replaced by Matthews after being assisted from the field by trainer Andrew Gray.

In the 70th minute, Cooper Cronk scored a try under the posts that was sent upstairs for review and the video referee took one minute and 21 seconds to confirm the on-field referees' original decision as a try.

While the game clock was stopped, Thompson's 15 minutes to return to the field to maintain a free interchange continued to count down.

The game clock was also stopped on three other occasions when Melbourne rushed in for a scrum in the 77th, 78th and 79th minutes for a total of one minute and five seconds.

While it could be argued the Dragons, who finished the game with 15 fit players, could have managed their interchanges better, Nightingale said the NRL should scrap its current guideline and make all concussion-related substitutions free interchanges.

"Make it a free interchange, that's it," he said.

"If you're going to do the right thing by the book, make it a free interchange whether they are ruled out or not. Get rid of the timed rules and make it so that you're not punished for doing the right thing by your player."

Dragons fullback Josh Dugan echoed Nightingale's sentiments.

"To punish a team for abiding by the rules for players' safety, I think that's a bit unfair," Dugan said.

"I definitely feel it shouldn't be used as an interchange. The rules are there for the players' safety, and that's fair enough. But when teams are getting punished and having to finish games with 12 players on the field, that's hard to cop."

How it happened

65.11: The referee calls time off as Joel Thompson, who appears to have suffered a head knock, is treated by a Dragons trainer.

65.58: The 15-minute concussion assessment period begins when Thompson is brought to the Dragons club doctor, who then begins testing. At the end of the 15 minutes, the interchange would count if Thompson didn't return to the field. (Time to go: 15 minutes)

69.13: One minute and 21 seconds elapse off the concussion clock when the game is stopped for a video review of a possible Cooper Cronk try. When the try is awarded there is 10 minutes and 24 seconds remaining on the concussion clock. (10:24)

76.11: The game is stopped for 23 seconds to pack a scrum after a forward pass by the Dragons. When play resumes, the concussion clock still has three minutes and three seconds remaining. (03:03)

77.45: The game is stopped for 26 seconds after Melbourne rush to pack a scrum following a Jason Nightingale knock-on. When play resumes, the concussion clock still has one minute and three seconds remaining. (01:03)

78.15: The game is stopped for 16 seconds after Melbourne rush to pack a scrum following a Billy Slater knock-on. When play resumes, the concussion clock still has 17 seconds remaining. (00:17)

78.32: The Dragons are forced to take a player from the field (Dan Hunt) and play the final 88 seconds with 12 men because they had used up all of their 10 interchanges. When the 15 minutes elapsed, Thompson's exit from the field was deemed to be their 11th interchange, therefore a player had to be removed from the field. (00:00)