Australia's talisman - and one of our only previously fully fit stars - left the pitch injured in Hertha Berlin's 3-1 loss to Bayer Leverkusen.
Leckie walked off the pitch on 54 minutes after a break in the match for treatment, with the full extent of his injury - rumoured to be hamstring - still to be confirmed by the club.
Leckie was heavily involved in the match until that point, drawing praise from the club across Twitter, who called the injury a "hammer blow".
"Given the injury misery, we should be happy with our 24 points so far. I hope Mathew Leckie is the last case," Hertha coach, Pal Dardai said after the match.
Pause. Durchpusten, den Kopf freimachen, und dann noch einmal 45 Minuten alles, aber auch alles raushauen. Dann geht hier definitiv noch was, Herthaner! 🔵⚪— Hertha BSC (@HerthaBSC) December 22, 2018
----- #B04BSC 2:1 #hahohe pic.twitter.com/ryLqlmyjjZ
The Asian Cup is now less than a month away and the Socceroos are supposed to meet up for a lengthy training camp under Graham Arnold in late December.
Leckie now joins Aaron Mooy, Tom Rogic and Daniel Arzani on the injury list for Australia, although Rogic (who has largely recovered) and Mooy have been named in Arnold's squad.
The 27-year-old has only recently worked his way back into the Hertha lineup after a hefty injury layoff, playing at least 80 minutes in each of previous four matches, roughly tripling his entire season's minutes until this point.
Not good news watching @HerthaBSC Mathew Leckie is coming off injured in what looks like a hamstring strain or upper leg muscle injury. Had been excellent again up to the injury. Hopefully not too bad as it would be a massive blow to our Asia Cup chances. #socceroos— John Grimaud 🇦🇺⚽️ (@grimaud_john) December 22, 2018
Leckie's loss would be a huge blow for the Socceroos despite Australia boasting substantial depth in Leckie's position, none play at a similarly high club level and few have proven goalscoring capabilities.
Possible replacements for Leckie include Awer Mabil, Craig Goodwin, Andrew Nabbout and Dimitri Petratos.