MELBOURNE, Australia — Novak Djokovic has had a walkover into the Australian Open quarterfinals after Jakub Mensik withdrew 24 hours ahead of their scheduled fourth-round match with an abdominal injury.The tournament confirmed Mensik’s withdrawal late Sunday. The match had been scheduled for Rod Laver Arena on Monday night.“After last couple of matches, I started to feel worse, and actually the problem is my abdominal muscle on the left side,” Mensik said in comments published by the tournament. “Like I said, last few matches it got significantly worse, and I think if I would step on the court tomorrow, it would be such a big risk for me for my next weeks, for my next tournaments, and actually for my health.”No. 16-seeded Mensik beat Ethan Quinn in straight sets on Saturday. He was the second player in as many days to withdraw before a match because of an abdominal injury, with Naomi Osaka pulling out of her fourth-round match on Saturday night.Novak Djokovic has won the Australian Open a record 10 times and is a 24-time major winner. He became the first player to reach 400 wins in Grand Slam singles when he beat Botic van de Zandschulp 6-3, 6-4, 7-6 (4) on Saturday night in the third round.Djokovic will be content with a night off as he con …