The improving centre-half limped off with 10 minutes remaining of Saturday's 1-0 defeat to Tottenham and adds to The Whites problems ahead of the trip to Southampton.
Definitely out is skipper Dominic Matteo, who serves a one-match suspension, while there is a doubt over the availability of Mark Viduka.
The Aussie returned home at the weekend to be at the side of his critically-ill father, who is understood to have a brain tumour, with Gray allowing him as much 'compassionate leave' as is necessary.
Zoumana Camara could now be recalled to the defence. The on-loan Frenchman has not figured under Gray since his first game as caretaker, a 2-0 home defeat to Bolton on November 22nd.