The player managed just nine appearances for the Highlanders last year, but has come off the bench three times this term.
Cooper said: "We are still trying to find out the toll the injuries have taken on Steve's knee.
"We would be worried about paying money for a player who might break down six weeks from now.
"Everything was rushed on Friday in the hope of signing Steve before our game on Saturday, and the doctors couldn't guarantee he had recovered fully from his injury problems.
"Steve has gone back to Inverness, but we still hope to sort something out, provided we can get assurances about Steve's health."