The British No 1 was trailing Uruguayan Pablo Cuevas 7-6 (3) 6-3 2-1 when he called for the trainer, flexed his left knee a few times and shook hands with his opponent.
Speaking in his post-match press conference, the 24-year-old from Beverley said: “I just wasn’t happy with my knee. So I didn’t feel it was obviously right to carry on.
“I’ve been dealing with it for quite a while. So it’s not anything new. It’s just been having to manage it.”
Edmund did not want to expand further on the issue, which first surfaced at the end of last season when he pulled out of his final event, the Paris Masters, citing fluid behind his knee.
Asked whether he could be a doubt for Wimbledon, he said: “Obviously I hope not. I’ll try and do everything I can. But it’s not like this is what you’ve got to do, this is how you’re going to get fixed, or this is the time.
“You just have to do the best you can and do rational things to get it better. This is professional sport. You’re dealing with things every day, so it’s nothing new.”
Edmund began this season as scheduled in Brisbane but suffered a surprise loss to Yasutaka Uchiyama and then withdrew from the Sydney International.
Although he took to the court at the Australian Open, he did not look fully fit and was well beaten by Tomas Berdych before taking a six-week break from the tour.
He has been playing regularly since then but has not found his best form and had lost five matches in a row on clay prior to a first-round win here over Jeremy Chardy.
That took two days and more than four hours and appears to have taken its toll.
Edmund said of the pain: “It fluctuates. Sometimes you feel good, sometimes not. Obviously, your workload can affect it. So playing a long match the other day has a bit of an impact on it as well. So it’s just constant management of it and trying to deal with it the best you can.”
Edmund said surgery would be “the last resort”, adding: “I don’t think it’s a big thing long term. But, when you’re playing professional tennis and the speed and the physicality that you play, if something is bugging you a little bit, it makes a little bit of a difference to your performance.”
Although it was not obvious that Edmund was struggling physically, it was certainly a curiously passive performance from the British No 1, who had been hoping to reach the third round for the third successive year. Cuevas is a classic clay-courter having played most of his season on the surface, with plenty of success, but the surprise was that he was the aggressor and the one dictating points.
Edmund has only won six tour-level matches this season compared to 19 by this stage last year and is in danger of dropping out of the top 32, meaning he would be unseeded at Wimbledon.
But he is a phlegmatic character, and he said: “I wouldn’t say it’s been terrible.”