Andy Murray apologised to the crowd at the Canadian Open after withdrawing from the tournament with an abdominal strain.
The 36-year-old Briton was due to face Italian seventh seed Jannik Sinner in the last 16 after beating Max Purcell in the second round.
Addressing the fans in Toronto, he said: "I feel like I've let you down."
Murray added: "This might be my last time playing here as well. So to finish like this feels rubbish."
The Canadian Open alternates between Toronto and Montreal, so the men's event will be staged in the latter next year.