Both the Swiss and Canadian endured lengthy injury spells during the 2017 season.
Anderson and Rublev replace Wawrinka and Raonic at Mubadala World Tennis Championship
Three-time grand slam champion Stan Wawrinka and former Wimbledon finalist Milos Raonic have withdrawn from the 2017 Mubadala World Tennis Championship (MWTC) and have been replaced by South Africa's Kevin Anderson and Russian Andrey Rublev.
Wawrinka has not played competitive tennis since his first round defeat at Wimbledon in July, with the 32-year-old Swiss undergoing surgery to fix a knee injury, and MWTC has come too early in his recovery.
“Unfortunately I won't be able to play in Abu Dhabi this year as I'm not ready yet to compete at this level," said Wawrinka, a four-time veteran at MWTC.
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"Together with my team, I'm working hard and we will do everything to be ready in time for the Australian Open. I'm sad that I won't be able to play in front of the great fans at the Mubadala World Tennis Championship but I need to be patient and give my body the time it needs.
"I wish everyone a great event and hope to be back in Abu Dhabi in 2018.”
Replacing Wawrinka is 2017 US Open finalist Anderson, who will face Spain's Pablo Carreno Busta on Day 1 of the tournament. The winner will take on world No 1 Rafael Nadal in the semi-final.
“I am looking forward to playing in Abu Dhabi and getting ready for the new season and the year’s first grand slam," said 31-year-old Anderson, who has made one previous appearance at MWTC, in 2016. "The competition is going to be intense and I’m looking to pick up on where I left off last year.”
Raonic, 26, also struggled with injury throughout 2017 and called his season early following the Japan Open in October. The Canadian world No 24 has twice competed at MWTC, reaching the final in his debut year in 2016.
Stepping in to replace Raonic will be 20-year-old Rublev, who enjoyed a breakout season on the ATP Tour in 2017 when he advanced to the quarter-finals of the US Open. Ranked No 39, Rublev claimed his first ATP Tour title at the Croatian Open and reached the final of the Next Gen ATP Finals.
“I am happy to be invited to an event of this level and it is a great honor for me," Rublev said. "I will do my best to show my top game and I am looking forward to meeting the local audience.”
Rublev will take on Austria's world No 5 Dominic Thiem in the quarter-finals, with the winner set to face 14-time grand slam champion Novak Djokovic in the semi-finals.
MWTC is a six-player invitational tournament that takes place over three days in Abu Dhabi. Day 1 sees the four lowest-ranked players contest two quarter-finals, with the two highest-ranked players taking on the respective winners in the semi-finals on Day 2. The last day comprises the third-place play-off and final.
Nadal is the defending champion having defeated Belgium's David Goffin in last year's final. The Spaniard is also the tournament's most successful player, lifting the trophy four times.