Mo Farah was non-committal about his plans for the future after being beaten by club runner Ellis Cross on his return to action at the Vitality London 10,000.
Farah was racing for the first time since failing to qualify for the Tokyo Olympics last June while battling a foot injury, and he was unable to outkick 26-year-old Cross over the final stages.
Farah, 39, finished a minute outside his best time on the road set over the same course in 2010, and declined to say whether he will target the World Championships in Eugene in July.
Speaking to the BBC, the four-time Olympic champion said: “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?”
A leading group that also included Chris Thompson was whittled down to two, with the unfancied Cross emerging victorious in a time of 28 minutes 40 seconds, with Farah second in 28mins 44secs.
Having made the switch to the marathon, Farah turned his attention back to the track in 2020 with an Olympic swansong in his sights, but this performance does little to indicate he can get back to an elite level.
“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.”
Cross was left stunned by the outcome, saying: “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. He’s known around the world, and I’ve just beaten him over his prime distance. I didn’t quite follow the script today but, to pull it off, I’m delighted.”
Victory in the women’s race went to Eilish McColgan, who finished just two seconds shy of Paula Radcliffe’s British record, posting a time of 30:23.
The Scot has had a great start to the season having broken Radcliffe’s British half-marathon record in February before improving her own five kilometres record in Malaga last weekend.
McColgan said: “I’m really, really happy with today. Obviously I’m disappointed to just miss it, but it is what it is, and hopefully I’ll have another couple of opportunities this year.”