Singapore's first SEA Games marathon champion in 30 years will not defend his title when the biennial meet comes to the Republic's shores in June.
The injury-stricken Mok Ying Ren, who triumphed at the 2013 edition in Myanmar in 2hr 28min 36sec, had initially earmarked this Sunday's Seoul Marathon to meet the qualifying mark of 2:30:30.
His personal best is 2:26:30, clocked at the Gold Coast Marathon in 2013, while his season best is 2:53:42, set at last year's Standard Chartered Marathon Singapore (SCMS).
This paves the way for Soh Rui Yong and Ashley Liew, Singapore's two fastest marathoners this season, to earn the nod to represent the nation in June. Soh clocked 2:26:01 on his debut last December, while Liew was timed at 2:32:12 in January.
Yesterday, Mok told The Straits Times that he had come to this "hard" decision after discussions with Australian coach Lee Troop.
In 2012, he decided to put his career as a doctor on hold to pursue his dream of running at the 2016 Rio de Janeiro Olympics.
"This is one of the most difficult choices I've had to make. The SEA Games is one of the events I was most looking forward to since I drew up my four-year plan," he lamented. "It's very hard. (Because of this) I can't sleep, and I've cried. It's a hard decision but one which will (improve) my chances in the long run."
Mok had also informed the Singapore Athletic Association (SAA) of his decision, saying: "I've already spoken to a few people in the SAA. They were supportive and respected my decision."
While his will to win was never in doubt, a couple of ill-timed injuries forced Mok to give up the historic chance of defending his title on home soil.
After recovering from a shin injury in October, which forced him to sit out last July's Commonwealth Games, he suffered an injury to his left gluteal muscle in December, just a week after making his comeback at the SCMS.
Mok, undergoing national service as a medical officer, rates his present fitness as "95 per cent".
He said: "Qualifying for this SEA Games (would have been) a rush because I haven't even started full training. I'm slowly trying to get out of this injury pit.
"Last year, every step I took, I was always thinking, 'Is this messing up another part of my body?' It's mentally draining. When people ask me how things are going, I was sorry because I felt I wasn't performing as well as I can."
Mok said he is grateful to the Ministry of Defence, sponsors including Pocari Sweat, Brooks, and AirAsia, as well as the National University Health System, which approved his one-year no-pay leave request to train in the US.
After completing his NS next month, Mok will head to Colorado to train at the Boulder Track Club for a year.
His sister Ying Rong, also a marathoner, will likely join him.
At Boulder, where the elevation in some areas is 2,400m, he will undergo high-altitude training with Troop, a three-time Olympian, and alongside runners aiming to make the US Olympic squad, as he zeroes in on the Olympic "B" time of 2:18:00.
Mok, who hopes to be able to race in May, said: "The climate there is cooler, the terrain is better, they have nice trails, (all of) which play a big part in injury prevention.
"(Troop) has a good track record of getting people with my times to sub-2:20 times. I just want to go there in one piece, try to stay healthy and do as much running as possible."
Mok said as difficult as the past year has been, he will try to take it positively. The runner, who also won the SEA Games triathlon gold in 2007, said: "In a way, it's good that it happened now instead of next year.
"I understand my body better, and I'll use this period to find the root cause of all these injuries.
"I also learnt that in sports, success is not guaranteed. You might do everything correctly, but a lot of things can happen that are not within your control.
"The idea is that it's okay to fail, but you have to keep trying."