Hyeon Chung has shared a photo of the blister that forced him to withdraw from last night's Australian Open semi final.
Chung had to retire during the second set after taking a medical time out, with Federer leading 6-1 4-1 at that point.
His foot was what was causing him grief, having had a series of blisters on his sole over the past week.
Chung explained after the match that his foot was in too much pain to continue, sharing a photo of the aftermath.
"Tonight, I tried very hard to bring my utmost energy to the tennis court as usual," he wrote on Instagram.
"However, I had to make a tough decision given that I cannot compete 100% against Roger, in front of many tennis fans. Please understand.
"I wish all the best luck for @rogerfederer in the finals."