WELLINGTON, New Zealand (AP) — Symptoms of concussion are complicating the Super Rugby return of All Blacks hooker Dane Coles following knee and calf injuries.

Chris Boyd, coach of the Wellington-based Hurricanes, says Coles is experiencing exercise-induced headaches which are making it difficult to train sufficiently to recover from other injuries.

Boyd said team medical staff and Coles have no idea when his concussion occurred. Coles injured his knee in a March 18 match against the Highlanders and aggravated a calf muscle injury in training.

Headaches began when he returned to training but medical staff, studying match videos, cannot find any incident in which he might have sustained head trauma.

Boyd said it was difficult for Coles to test the recovery of his knee and calf while concussion symptoms persist.