Defender Zoumana Bakayogo has returned to parent club Leicester City after rupturing an anterior cruciate ligament during his loan debut for Yeovil.
The 27-year-old was taken off in the first half of Saturday's 2-0 win over Birmingham after appearing to catch his studs in the turf.
"Zoumana said he just felt his knee crumble under him," Glovers manager Gary Johnson told the club website.
"It was innocuous - he just turned and he felt it."
Bakayogo was replaced on 37 minutes by Jamie McAllister, who himself pulled up injured shortly after the break.
"We brought in Bakayogo for Liam Davis, who we left at home because he was injured. So there's maybe another little left-back hunt again in the next week or so," Johnson added.
Championship strugglers Yeovil have had a run of bad luck with injuries to loan players this season, after previously losing Manchester United goalkeeper Sam Johnstone, Wigan midfielder Fraser Fyvie, Swindon striker Andy Williams and Bristol City defender Liam Fontaine.