ATP Finals champion Medvedev will take on compatriot Andrey Rublev in the next round after the No. 7 seed’s opponent Casper Ruud retired injured.

“At least one of us will be in semis, that’s good news,” said Rublev, who was 6-2 7-6 (3) ahead when Ruud handed him a walkover win.

“Last time he beat me in the quarter-final of the US Open and now we meet in the quarter-finals of Australian Open, we’ll see what happens.

“I hope we can show great level and it will be a great battle.”

World No 192 McDonald had some luck going to the net but could not match the power of Medvedev’s serve or the intensity the Russian brought to bear on big points.

“I played a great match, was feeling the ball great, serving great, hit some good winners,” said the 25-year-old. “I was feeling really good out there. That’s the most important thing.”

Rublev spent only 80 minutes on court in the clash of two former junior world No. 1s because of Ruud’s retirement, which came after the Norwegian lost the second set tiebreak.

“I feel sorry for Casper,” said 23-year-old Rublev. “I hope he recovers real quick. I did not expect it to end this way, but this is sport.

“”I’m feeling perfect,” he added. “I’m feeling physically great.”

Qualifier Aslan Karatsev could make it two Russians in the last four if he beats Grigor Dimitrov in the quarter-finals on Tuesday.