EX-SYDNEY co-captain Kieren Jack has been ruled out for at least the next fortnight due to a nagging hip injury.

After collecting 21 and 19 possessions respectively in the opening two rounds, Jack has managed between 12 and 14 disposals in his last three hit-outs – well below his usual output.

Swans coach John Longmire said Jack's ongoing hip concern was the cause of his sudden form slump, but did not put an exact timeframe on the 29-year-old's return.

"We've been playing him now for five weeks and it's not getting better, it's getting worse," Longmire told Fox Footy on Monday night.

"He needs at least a couple of weeks off and hopefully (with) some rest and recovery over the next few weeks, we'll be able to get him back into good form and get him fit and firing for the rest of the season."

Jack missed the entire JLT Community Series due to the hip issue, and has struggled to adjust to a new role predominantly up forward this year.

Essendon great Matthew Lloyd told AFL.com.au's Access All Areas on Monday that Jack may have "fallen off the cliff" and should be demoted to the NEAFL.

Jack had a very public falling out with his parents last July, which overshadowed his 200-game milestone against Geelong in round 16.

He has played 215 games for Sydney and kicked 147 games since debuting in round six, 2007.