The Leeds United midfielder is in the early stages of his recovery and preparing to miss much of this season having seen his spell at Bundesliga 2 club Greuther Furth halted last month.
Ideguchi was a handful of appearances into his year-long stay with the German club when he limped out of a 1-0 win at Dynamo Dresden on September 30.
The Japan international was diagnosed with a damaged posterior cruciate ligament (PCL), the same injury sustained by Leeds forward Patrick Bamford.
Bamford is out until January at the earliest and Ideguchi looks set to be missing until the spring, despite avoiding the need for an operation.
Leeds sent him to Germany in search of regular football and some impetus after an unrewarding start to his career at Elland Road.
Ideguchi, who moved to England from Gamba Osaka in January, finished last season on loan at Spanish club Cultural Leonesa but a lack of game time there cost him his place in Japan’s squad for the World Cup.
Leeds head coach Marcelo Bielsa chose not to involve him in his first-team squad this season and Ideguchi left for the continent shortly before England’s August transfer deadline.
He made just three starts for Greuther Furth and his injury is another blow to his hopes of finding his feet in Europe.
Ideguchi is the second United loanee to suffer a serious injury after Eunan O’Kane was ruled out for the rest of the term by a double leg fracture.
O’Kane underwent surgery having been hurt in a League One game bewteen Luton Town and Bristol Rovers on September 15.
O’Kane had moved to Luton just two weeks earlier and was making his fourth appearance.