Star Wallaby fly-half Quade Cooper is set to miss next month's Test series against France after a shoulder injury in the Queensland Reds' 30-27 Super Rugby loss to the Melbourne Rebels in Brisbane on Saturday.

Cooper is facing at least a month on the sidelines after being diagnosed with a grade three AC separation from a jolting hit on his left shoulder just after setting up an early try to Mike Harris.

With Test coach Ewen McKenzie to name his 32-man Wallabies' squad to face the French on Thursday, the timing couldn't be worse for Cooper, who was likely to start in the first of three Tests in Brisbane on June 7.

The 50-Test flyhalf was on the field for just eight minutes before landing heavily on his shoulder in a heavy tackle by Rebels pair Laurie Weeks and Tom Kingston.

“I knew there was something wrong,” Cooper said.

“I heard a bit of a crack and I could feel that my shoulder wasn't sitting right so I was told I had dislocated my AC joint.”

Cooper's setback opens the way for ACT Brumbies' playmaker Matt Toomua to take his place in the Wallabies' starting lineup against the French.– AFP