Adelaide United captain Eugene Galekovic will miss about four weeks because of a rare shoulder injury.
Galekovic was forced from the field during the Reds' A-League loss to the Central Coast Mariners last Sunday but the exact nature of his injury is puzzling Reds medicos.
Scans revealed an ailment previously unseen by Adelaide's doctor and physiotherapist, a club spokesman says, adding it isn't a simple muscle tear.
The injury to Galekovic's right shoulder is the latest misfortune to hit the struggling defending champions, who are last on the A-League ladder with just two wins.
Galekovic will miss Adelaide's initial games in the Asian Champions League (ACL) -- their Asian campaign starts on Feb. 22 with a home fixture against Gamba Osaka.
But the Reds have bolstered their squad with the signing of South Korean international Kim Jae-sung.
And Senegalese forward Baba Diawara is awaiting final approval of a work visa to join the club, and Eli attacker Babalj has also been signed by the Reds for the rest of the domestic season and the Asian campaign.
The signings follow Adelaide's three new recruits -- fringe Socceroo James Holland, Spaniard Sergi Guardiola and striker Henrique -- all leaving the club midseason.
South Korean Kim is a 33-year-old midfielder who represented his country at the 2010 World Cup.
Kim played mostly for Korean powerhouses Pohang Steelers but recently had a stint on loan at Jeju United -- one of Adelaide's group opponents in the looming ACL.
"One of the main reasons for joining Adelaide was to get to play in the champions league with this club," Kim told reporters on Wednesday.
"We're in the same group as my old club ... so it's going to be weird, it's going to be a different experience.
"But no matter which club I play for, I'm out there to win."