Cape Town - Chiefs centre Sonny Bill Williams has been suffering from headaches and looks unlikely to feature in their Super Rugby clash against the Sharks in Durban on Saturday.
Williams clashed heads with Stormers prop Vincent Koch in the 17th minute of their match at Newlands last weekend, but was cleared to continue playing after undergoing a concussion test.
Since the match, however, Williams has failed to recover from the knock and has complained of headaches, the Stuff.co.nz website reports.