BBC News reports that David Tennant was unable to take part in last night's performance of the current Royal Shakespeare Company production of Hamlet at the Novello Theatre in London, due to what is described as "a long-standing back injury".
The play transferred to London last week following a successful run at Stratford-Upon-Avon. Tennant's understudy Edward Bennett took the role for last night's performance.
UPDATE: The Guardian and many other sources are reporting an official RSC press release that Tennant has not been well enough to resume the role for this evening's press night. The performance will once again see Bennett as Hamlet.