As Jack Draper retires from his Australian Open fourth-round match, BBC Sport analyses the key questions around his injury issues.

Carlos Alcaraz reached his 10th career Grand Slam quarterfinal, tied for the most by a man before his 22nd birthday, by advancing at the Australian Open when 15th-seeded Jack Draper stopped playing because of injury after dropping the first two sets Sunday.

Draper had pushed his once-fragile body to new extremes with three five set matches in a row, each time coming back from two sets to one down.