Chiefs centre Sonny Bill Williams has been suffering with headaches and looks unlikely to feature against the Sharks in Durban on Saturday.

Williams clashed heads with Stormers prop Vincent Koch in the 17th minute of last Saturday's match, but was cleared to continue playing after undergoing a concussion test.

However, since the match, Williams has complained of headaches, and has yet to begin the concussion protocol that would allow him to play.

'He hasn't recovered as quickly as we would have liked,' said Chiefs assistant coach Tom Coventry. 'He's had a few headaches, and he's under a bit of a selection cloud. There's a pretty comprehensive list of events he has to go through to be able to play.

'It's a five-day process, so he'll have to make some progress by tomorrow, or even this afternoon.'

The Chiefs will also be without Tim Nanai-Williams for the match at Kings Park, after he was sent home with a broken finger, while prop Pauliasi Manu is struggling with a rib injury.

Marty McKenzie has been drafted in as cover for the departed Nanai-Williams, while a decision will be made on Manu later this week.

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