Colosimo was sent off in the 80th minute of last week’s 1-0 win over Wellington Phoenix in Palmerston North and it seemed clear that Sydney officials would appeal the one-match suspension because the incident was not severe.
But the club took no action meaning the 30-year old will have to miss the top of the table clash in Melbourne at Etihad Stadium.
''For the club to decide not to appeal, I don't think was [right]. At least we should have given it a go. If they [the appeals committee] reject it, they reject it. If there was that slightest chance of having it overturned, I'd hope we'd have done it, so I'm pretty disappointed,'' he told the Herald.
''The way I see it, what's the worst thing that could have happened? It's the biggest match of the season so far - not only for the club but the whole league - and I wanted to be part of it.''
Colosimo said that the club did not believe they had a strong enough argument to contest the verdict but he said they at least should have attempted to help get him off.
''They weren't too optimistic that it would get overturned,'' he said. ''I don't think they or anyone else who saw it would think there was a chance it could be extended, so it wasn't that. I think they thought there was only a 30 per cent chance that it could get overturned. But for me that 30 per cent, considering this game coming up, was more than enough.''
The Australian international believed he was harshly done by when he was sent off last weekend but concedes that now it is all done and dusted, he just has to get on with it.
''I was really stunned. I didn't feel like it was a red and in speaking to a few of the boys, the angle the ref was at may have cost me but that's part of the game,'' he added. ''Yet after the challenge nobody from the other team got up for the old scuffle. Usually if there's a naughty tackle that ensues.
''That was his interpretation though and that's fair enough. It's pointless arguing on the pitch but there was the option to appeal and we didn't. So be it, now we move on.''