British distance great Mo Farah was noncommittal about his athletics future after being beaten by a club runner on his return to action at the London 10,000 (metres) on Monday.
The four-time Olympic champion, racing for the first time since failing to qualify for last year's Tokyo Games while struggling with a foot injury, was unable to out-kick Ellis Cross, 26, over the closing stages.
Farah, 39, finished a minute outside his best time over the same course in 2010, and then declined to say whether he will try to compete at the World Championships in Eugene in July.
The 5,000 and 10,000 metre champion at both the 2012 London and 2016 Rio Olympics, Farah told the BBC: "Your body has to be ready. You have to be in the right frame of mind. You have to be able to compete with the guys.
"Today was a tough day. Ellis did really well to win here. But you've got to see where you are.
"At the minute I don't even know. You've got to take it race by race and let the body see what it can do. I'm not getting any younger, am I?"
Farah moved up in distance to the marathon only to move back to the track in 2020 as he aimed for an Olympic finale but Sunday's performance could hasten the end of his career.
"I did put some good blocks of training together but it's been so, so long -- nine months since my last race," said Farah. "I love the sport and I love what I do.
"I've had a long career but there's a lot of youngsters who are coming through, which is nice to see."
A stunned Cross, left struggling to take in his victory, said: "I didn't believe it until 20 metres from the finish, I was like, 'He's just going to outkick me, that's just that'. I can't explain the feeling. It's overwhelming.
"The most inspiring thing for myself is I've beaten somebody that's an idol."