The winger is facing time on the sidelines after sustaining ligament damage to his ankle and the Gers coach confirms there is no break, but admits it's a bitter blow for the side
The 23-year-old was stretchered off during the Gers' Third Division stalemate versus Annan, and scans have since revealed the extent of his injury.
McCoist also divulged that there has been no break, but has said the player will require further tests before a time frame for his return can be set.
"David has obviously got a very sore one. The good news is that it's not broken," McCoist told Sky Sports.
"He has been for an X-ray but there is massive swelling and there looks to be a good bit of damage to the ligaments unfortunately.
"We are waiting on the swelling going down and then David will get a scan in the next few days.
"I couldn't put a timescale on the return from injury unfortunately but it's not great."
The young winger, who only recently arrived from Hearts, was fast becoming an important player for the Ibrox outfit and McCoist admits it is a bitter blow for the team.
The 49-year-old coach added: "We were delighted to get wee Temps [Templeton] in because he was without doubt our number one target in the window. He creates things and scores goals.
"It's a bitter blow for us but it's something we have to handle and get on with."