Riordan claims that club doctor Derek McCormack told him to stay away from the other players to prevent the illness from spreading.
However, the club fined the striker the next day and Players Union representative Fraser Wishart has been called in to help resolve the dispute.
Celtic have since issued three further demands for payment from Riordan, whose furious outburst at his manager at the weekend is likely to signal the end of his Parkhead career - should Strachan stay in charge.
