Canada's Denis Shapovalov says he would not have been able to forgive himself if the umpire he hit in the eye with a ball had been seriously injured.
Shapovalov was fined $7,000 (£5,600) for his actions during a Davis Cup match with Great Britain's Kyle Edmund.
The 17-year-old trailed 6-3 6-4 2-1 when he struck the ball in anger and hit Arnaud Gabas, defaulting the match.
"I know how dangerous it can be to fire a ball," he told the BBC. "My first concern was that the referee was OK."
Speaking to BBC Radio 5 live Breakfast's Nicky Campbell, he added: "I turned over and saw the official bending down, holding his eye. So from that moment on I was in complete shock and regret right away.
"I kind of blacked out for the next 10 minutes maybe. I remember going to the bench, asking if the ref's OK."
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Shapovalov, who escaped the maximum $12,000 (£9,600) fine because it was deemed to be unintentional, said he spoke to Gabas after the match and the French umpire even managed to "joke around a little bit" regarding the incident in Ottawa.
Gabas went to hospital as a precaution but no damage to the cornea or retina was found. He was due to see an eye doctor in France for a further examination.
"I've been hit several times in the eye and other parts, so I know how dangerous it is," added world number 251 Shapovalov.
"I'm very lucky he is OK. If things had gone worse I don't think I would have been able to forgive myself and I don't think I would be able to move past it.
"I'm hoping I'll learn from it and move forward so that it is a lesson for me."
The teenager also apologised to Edmund and and the British fans, saying he was "odds on" to lose match before he was disqualified.
"I feel bad that I didn't allow the British team to have the celebration that they deserved," he added.