Sydney - Wallaby James O'Connor is expected to miss up to two weeks of Super Rugby after injuring his shoulder playing for the Rebels this weekend.
The Rebels said on Sunday that the Wallaby playmaker damaged his left sternoclavicular joint, although scans showed there was no fracture.
O'Connor's setback comes just weeks ahead of the British and Irish Lions tour to Australia - he is vying with Quade Cooper and Berrick Barnes for the Wallabies flyhalf role.
O'Connor was injured in the early stages of the Rebels' 36-32 loss to the Blues in Auckland on Saturday and initially played on.
But four minutes later he was slammed on to his back by Rene Ranger as he set up a try for centre Frances Saili and had to leave the field.
Meanwhile, Barnes came off the bench to kick the crucial conversion and a 50m penalty to seal the Waratahs' 21-15 win over the Stormers in Sydney on Saturday.
The one-time Wallabies vice-captain has played a total of only 35 minutes all season but he has come back into reckoning for the Lions Test series after returning to action from a wrist injury.
Barnes has another chance to impress for the Waratahs against Super Rugby leaders the Brumbies next weekend before coach Robbie Deans names a 25-man Wallabies squad next Sunday (May 19).
Deans will unveil his final 31-man squad on June 11 to tackle the Lions.