World number four Alexander Zverev could be in doubt for the Australian Open after withdrawing from the World Tennis Challenge with a hamstring injury.
Zverev told the crowd at the two-day event in Adelaide that he injured him hamstring training on Monday and would sit out the tournament.
The 21-year-old German didn't go into detail about how serious the injury was but said he would be attempting to get it right for the Australian Open which gets underway in Melbourne next Monday.
Alex Zverev announces on court in Adelaide that he has pulled his hamstring during practise today and says he will rest and aim to be ready for Melbourne.
— Nick Lester (@nicklester) January 7, 2019
Spanish veteran Fernando Verdasco will replace Zverev in Monday night's men's singles match against Borna Coric at the World Tennis Challenge.
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Zverev is currently the fourth favourite with the bookies to take out the first major of the year and is coming off the back of a win at the season-ending ATP Finals in London.
He knocked off Roger Federer in the semi final before downing Novak Djokovic in the final to claim the title.
Zverev is yet to make the final four of a Grand Slam but many were tipping next week's Australian Open to be the one in which he went deep into the second week.
Any lingering injury is likely to be tested over the best-of-five set format at Melbourne Park.
Juan Martin Del Petro is one big name who has already been ruled out, with the Argentine fracturing his patella late last year.
The 107th edition of the Australian Open is the richest yet, boasting a total prize pool of $62.5 million.
