Sandaza suffered a broken cheekbone in the League Cup win over Mothwerwell in midweek, ruling him out for the rest of 2012.
McCoist shared his disappointment for Sandaza in his pre-match press conference.
He said: "I'm just gutted for the lad. It's a blow for Fran himself and I've been up to see him a couple of times in hospital.
"It's a horrendous facial injury and it's as bad as I've ever seen on a football park, it's a bit of a mess.
"Having seen him and spoken to the doctors and surgeons, that is certainly going to be a longer-term thing. He has got a really sore one."
Rangers begin life without Sandaza with a Scottish Cup tie against Highland League side Forres Mechanics this weekend.