Following a doctor's advice, the opening night at the Edinburgh Festival has been put back by one day to Aug. 7, with a press night on Aug. 12. Plans to transfer the production to London's Gielgud Theatre on Sept. 3 remain unaffected. In a statement producer Nica Burns said, "We so hoped to make the first performance, but poor Christian's chicken pox has simply been too virulent".

Slater plays the lead role of McMurphy, the part played by Jack Nicholson in the 1975 Milos Forman movie. Slater, whose film performances have been compared to Jack Nicholson, caught the virus from fellow cast member Felix Dexter, who was struck down in the second week of rehearsals. Dexter has since made a full recovery.

The illness hits the production after Terry Johnson stepped in as a last-minute replacement for director Guy Masterston, who left the show citing personal reasons.