Andy Murray returns to action from a hip injury later to feature in an unscheduled match in Abu Dhabi.
The three-time Grand Slam champion replaces former world number one Novak Djokovic, who has withdrawn from the Mubadala event with an elbow injury.
Murray, 30, had initially planned just to practise at the event as he builds up to the Australian Open.
However, the Scot will instead play an exhibition match at 15:00 GMT against Spain's Roberto Bautista Agut.
Murray is due to fly to Brisbane in the next couple of days, where he is entered for the ATP event there.
It is not clear whether he still intends to contest that tournament before flying to Melbourne for the Australian Open, which gets under way on 15 January.
Murray, who has slipped to 16th in the world rankings, was beaten by America's Sam Querrey in the Wimbledon quarter-finals before travelling to New York in late August for the US Open, but he pulled out two days before the tournament began, having failed to recover sufficiently.
His last public appearance was at a charity match against Roger Federer in Glasgow in early November, where he took a set from this year's Australian Open and Wimbledon champion.