By Jennifer Witham

Gold Coast SUNS defender Michael Coad is in danger of missing the rest of the season after tearing his hamstring off the bone in an incident GC SUNS coach Guy McKenna claimed was at least partly caused by the substitute rule.

The injury was sustained after Coad had battled cramp in the third quarter of the match that resulted in a 90-point loss to Melbourne.

The 27-year-old was sent back onto the field in the final term, as the GC SUNS had already activated their substitute when Alik Magin was replaced by Daniel Gorringe early in the third quarter.

Coad broke down at the 10-minute mark of the final term and had to be helped off the Gabba with what McKenna revealed on Tuesday was a serious tendon injury that would require surgery.

Despite the outcome, McKenna defended the decision to keep playing Coad, and said he had been forced to send Coad back on the field by the substitute rule.

"It was either him or one of the other two blokes cramping as well," McKenna said on Tuesday.

"As a 27-year-old, it was unfortunate, but we had two younger kids out there.

"We would think that a 27-year-old is going to have a better chance of overcoming that and still having a leg to stand on rather than two young kids.

"It's not fantastic but what do you do? Play one short?"

McKenna was asked if he had offered his feedback on the rule to the AFL, but declined to answer as he said he was entering "dangerous ground".

While Coad is seeking a second opinion, he is expected to require an operation similar to those undertaken by St Kilda star Nick Riewoldt and Hawthorn's Josh Gibson last season.

Both sustained their injuries in round three and were able to return in round 15, but McKenna said Coad shouldn't expect a similar timeframe for his recovery.

"It's long term. Nick Riewoldt had that conditioning of eight or nine pre-seasons under his belt … Coady, I know he's a mature boy, but he's really only done one [pre-season]," he said.

"To miss [that long] and try to get him back for the end of the season – we're certainly going to keep that candle [alight] for him and make sure that's his goal – but history would be against him that's for sure."

Coad, a former SANFL backman with Sturt where he finished second in the best and fairest count in 2009, has played in two of Gold Coast SUNS three AFL games, collecting 20 possessions against the Western Bulldogs and 14 against Melbourne before he was injured.