Sydney coach John Longmire wants to put last Friday's interchange controversy behind him and concentrate on Saturday's clash with Western Bulldogs after receiving an apology from the AFL.

An interchange steward incorrectly ruled Sydney had 19 players on the ground late in Friday night's loss to Carlton.

The Blues were awarded a free kick and 50m penalty from which Carlton's Setanta O'hAilpin goaled.

That increased Carlton's lead to seven points and the visitors ultimately won by 16 points.

The AFL's umpiring department contacted Sydney on Monday to apologise after reviewing tape of the incident.

The footage confirmed Sydney had only 17 players on the ground when midfielder Dan Hannebery returned to the play.

"It is what it is now, we knew at the time we were right, it's been proved right," Longmire told reporters.

"Now we will get on with trying to beat the Bulldogs this week.

"It's not about who was right and who was wrong, it's just about whether the correct decision was made or not, and clearly the wrong decision was made."

Sydney suffered a setback on the fitness front Monday with key midfielder and reigning club champion Kieren Jack ruled out for 4-6 weeks with an ankle injury.

Longmire said Jack was backing himself to get back quicker than four weeks, but admitted his loss was a blow to the Swans.

"It's obviously disappointing for Kieren and the team, he's such an important player," Longmire said.

"I think he's getting back to some really good form, his first quarter on the weekend on Chris Judd was excellent."

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