Stan Wawrinka and Milos Raonic have both withdrawn from an exhibition event in Abu Dhabi as they continue their recovery from injury.
The pair were due to feature at the Mubadala World Tennis Championship that begins on December 28 but have been forced to pull out.
Both men struggled with injury problems throughout 2017, with Wawrinka unable to feature competitively since Wimbledon with a knee problem.
Raonic, meanwhile, struggled to maintain his fitness having started the season as world No. 3 and saw his ranking slip to 24th after retiring from his second-round match in Tokyo.
Both were in line to meet either Rafael Nadal or Novak Djokovic at the event should they have won their opening match, but pulled out altogether in a move that will cast doubts over whether they’ll be ready to feature at the Australian Open that starts in less than a month’s time.
Kevin Anderson and Andrey Rublev have stepped up in their absence, with the US Open runner-up facing Pablo Carreno Busta for a chance to face Nadal in the semi-finals, while Rublev will take on Dominic Thiem to set up a clash with Djokovic.
Both Djokovic and Nadal are returning from their own injury problems, with an elbow injury forcing the Serb out since Wimbledon, while a knee issue hampered the end of world No. 1 Nadal’s season.