American qualifier Brian Baker has been forced to retire though injury despite being a set up against Sam Querrey in their Australian Open clash.
Baker made the second round in Melbourne earlier this week after taking seven years off from the professional tour in a career blighted by a succession of injury problems.
Despite taking the first set on a tie-break in a gutsy display Baker went down early in the second with a leg injury.
After struggling to reach his chair Baker called for the trainer, and after expressing that he felt something pop in his knee was left with little choice but to retire and end his tournament.
Querrey tired to console his compatriot, who left court six in a wheelchair to hand his opponent a walkover to the third round.
The 20th seed will now face either Stanislas Wawrinka or Tobias Kamke in the last 32.
