SYDNEY Swans young gun Isaac Heeney is expected to be sidelined for up to six weeks after damaging the posterior cruciate ligament in his right knee against Melbourne at the MCG on Saturday night.

Meanwhile, Jake Lloyd and Dan Hannebery played out the game with ankle problems, with coach John Longmire praising Lloyd's effort after being particularly sore and confirming Hannebery was "OK".

Heeney is yet to undergo scans which will reveal the true extent of the injury, but Longmire was relieved the 19-year-old hadn't suffered a season-ending anterior cruciate rupture. 

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"Our doc thinks it's probably four to six (weeks)," Longmire told reporters post-match. "That's obviously straight after a game – he hasn't had a scan yet – but that's the early diagnosis … Hopefully that's a good sign."

Late in the second quarter, Heeney attacked a marking contest with typical vigour when he hurt his right knee. The fifth-gamer, who turned 19 on Tuesday, was unable to put any pressure on his right leg and appeared to feel intense pain behind the knee.

Heeney hobbled from the field aided by a trainer and was immediately substituted out of the game, replaced by veteran Adam Goodes.

The young Swan, who missed last weekend's loss to the Western Bulldogs with an ankle strain, had earlier been taken into the rooms for treatment for a different problem.

Heeney is the favourite for the NAB AFL Rising Star.