Bolton defender Tyrone Mears has been taken to hospital after breaking his leg in training on Thursday.
"Ty went in for a challenge and unfortunately suffered the injury," Trotters manager Owen Coyle said of Mears, who signed from Burnley in July.
"It was desperately unlucky for him and we will make sure he is fully supported in his rehabilitation."
Mears, 28, joins midfielder Lee Chung-yong on the sidelines after he also suffered a broken leg, on Saturday.
The South Korea player was ruled out for nine months after sustaining the injury during the pre-season friendly win at Newport County.
Another long-term Bolton injury victim, United States midfielder Stuart Holden, is still recovering from the anterior cruciate ligament damage he suffered in March.
Mears was set to take up the right-back slot for Wanderers but now it appears that either Gretar Steinsson or Sam Ricketts will have to fill in for him.
Coyle added: "He will go for a check and an assessment in a month and that will indicate more accurately the timescale for his recovery."