a knife in public, BBC reports.
Charly Martin, 21, from Guadaloupe, in the Caribbean, had been competing at an event in Thurso in April.
Wick Sheriff Court heard he had armed himself with the knife after he and three other surfers were attacked at a party.
Nike confirmed to the BBC Scotland news website that Martin had been dropped.
In a statement, a spokesman said: "Nike has ended its sponsorship of Charles Martin as a result of his recent conviction.
"We have no further comment."
Professional surfers
Martin was fined £500 at Wick Sheriff Court in September for carrying a knife in public.
The surfer was unaware it was an offence to carry a knife in public in Scotland.
The court heard that Martin and his friends, also professional surfers, were attacked at the party on 18 April.
He fled back to his hotel where he discovered one of his friends was missing.
Before going out to look for him, Martin armed himself with a long-bladed, serrated knife from a cutlery tray.
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