He's a last-minute replacement. After today, they'd have had to play with the original roster.
Done or occurring at the latest possible time before an event.
1962 April, J. N. Faulkner, “Summer Saturday at Waterloo”, in Modern Railways, page 263:
Instead, travellers are directed to the respective assembly points; this facilitates any last-minute changes in platform arrangements and also frustrates any would-be queue-jumpers.