A change in finals schedule in a COVID-disrupted season stipulated the top two sides in each senior grade would progress to the grand final.

Final round results initially saw Helensburgh leapfrog second-placed Figtree into the second division decider after the Crushers suffered a heavy defeat to Avondale.

However, the IDRL subsequently determined that Avondale had fielded a player ineligible due to suspension - ultimately changing the result to a forfeit. The two points awarded to Figtree saw them move past the Tigers on for and against into Sunday's grand final against minor premiers Wests.

Avondale - whose top side will contest the Open Age grand final on Sunday - issued a statement on Friday saying it had acted based on information contained in the online system.

"Our club registrar filled out our club's team sheets on the LeagueNet system and entered the player's name on the team sheet," the statement explained.

"This is not possible if a player is still currently suspended and unavailable to play as the online system prevents this action on a suspended player. Our player was cleared to play, we did not try and play a suspended player; or cheat.

"The league has acted as per their by-laws which we must accept, but we do not accept sole responsibility for this miscommunication and failure of the LeagueNet online system that all teams in the Illawarra Division are subject to. Our sincerest apologies must go out to the Helensburgh Tigers who have been dealt a great injustice due to this indiscretion."

While the online system cleared the player to be listed on the team sheet, the league determined that a bye in that four-week period did not constitute a match served under its by-laws.

Helensburgh skipper Jono Newman said the club's own investigations had reached the same conclusion as Avondale - that the online system indicated the player's suspension period had expired prior to him taking the field last week. It formed the basis of the club's appeal but the IDRL board ultimately upheld its initial decision on Thursday night.

"As a team we were pretty shocked, we thought it was a joke at first," Newman said.

"A lot of the boys have never had a chance to be in a grand final, there's a couple of guys who won't have a chance now because it's their last season.

"We knew the result of that [Figtree-Avondale] game and played our game based on that result. We gave a lot of players a run knowing all we had to do was win to make the grand final. It was a for and against [difference] we could have easily chased if required.

"Congratulations to Figtree, they haven't done anything wrong, I don't think any of the clubs have. It is what it is at this point, it's just a crap situation."