But Ledley has been given the all-clear from his specialist and is to return for Cardiff's Championship run-in.
Ledley hopes to return for Cardiff's Championship match with Reading on 10 April while full-back Mark Kennedy is having an X-ray on a rib injury.
The former Republic of Ireland international was forced off in Sunday's 3-1 win over Watford and joins fellow defenders Anthony Gerrard (calf) and Kevin McNaughton (thigh) on Dave Jones' injury list.
Ledley, meanwhile, has not played for the Bluebirds since their 6-0 win over Bristol City on 26 January.
And the Cardiff's Championship form has stuttered since Ledley and fellow experienced midfield partner Stephen McPhail were forced out with injuries.
The Welsh club have won five of their 11 league games since Ledley's last appearance and Jones' sixth-placed team are clinging on to the last play-off place.
But Ledley's admission that he could be back in three weeks - just after their South Wales derby with rivals Swansea City - is a major boost for boss Jones.
The Cardiff manager has long bemoaned his lack of strength and depth - especially in the key central midfield area - and his inability to sign reinforcements in the January transfer window due to Cardiff's well-documented financial problems.
McPhail made a welcome return for Jones in Cardiff's 2-1 win at Coventry last Tuesday and now Ledley may be available for selection for their final four potentially crucial run-in - starting with Reading's visit to the Cardiff City Stadium.
"Once he can start running, we're looking at three weeks all being well," said Jones.
"So some time in April we might have him back. With Joe, I'm trying to push the physios to force it along but they might tell me five weeks. It's just down to Joe.
"I think Joe wants to play again before the end of the season."
Cardiff fans feared academy graduate Ledley - who has now played almost 250 games for the Bluebirds - had played his last game for his home-town club.
As Ledley, who has captained both his club and country, is still in contract dispute with the club he has played for since age of nine.
The 32-times capped Welshman, who has attracted attention from top Premier League and Scottish clubs, is out of contract at the Cardiff City Stadium in the summer and has so far failed to agree terms on a new deal.
Source: BBC Sport
Source: BBC Sport