Rugby pundits have slammed Australia in the wake of their 28-27 loss to Italy in Florence, with former captain Stirling Mortlock (45) calling the result a "train wreck" and declaring Dave Rennie's side no chance of winning a third World Cup in France.
Asked about Mortlock's comments, McKellar said he was entitled to his opinion.
"Do I agree with it? 100 percent not," he told reporters.
"There's a good group of footballers here and there’s a core group of players that are still back in Australia as well.
"What you’ll find is the 33 (players) that go to the World Cup next year are certainly good enough to win that trophy."
Australia have lost eight out of 12 tests this season and face world number one Ireland in Dublin on Saturday.
McKellar defended the Wallabies staff for changing most of their starting 15 against Italy, saying it would be irresponsible not to rest players.
"Then you're throwing them under the bus at the most important time of the tournament," said McKellar.
"So you've got to develop (players). You'll see this week, like we did last week, we picked a team that we thought would beat Italy and we'll do the same this week with the Irish."
