Ahead of Mo Farah's much-hyped marathon debut in London on Sunday, few expert observers believed he stood any chance of winning.

But his lacklustre eighth place finish and modest time of 2hr 8min 21sec, which only puts him in the second-tier elite category and failed to even threaten a nearly 30-year-old British record, will be leaving the track star questioning if he has a future on the roads.

The lessons from his debut appear to be two-fold: firstly, the double Olympic and Worlds champion over 5,000 and 10,000m seems to be better built for speed, illustrated last year when he clocked the sixth fastest 1500m of all time.

Even his 5,000 and 10,000m golds have been more down to his wily racing tactics closed off with a staggering finishing kick, something that counts for little over 26.2 miles (42.2 kilometres).

Secondly, east African distance powerhouses Kenya and Ethiopia have raised the bar so high over the distance -- their top runners regularly clocking times below 2:05 -- that what was a good time a decade ago will now only leave you in the also-ran category.

On any given day, for every eight elite Kenyans and Ethiopians, one or two of them stand a chance of being in aggressive, record-breaking form -- as was the case in London on Sunday for Kenya's Wilson Kipsang.

"I will be back," Farah told the BBC after the race. "I'm not going to finish it like this. I gave it my all but I'm disappointed I didn't go out there and give what the crowd deserve."

However, the 31-year-old Farah -- who trained with the Kenyans at altitude for two months to prepare for London -- refused to be rushed into a decision on his future, saying: "I'm disappointed but you try things and sometimes it doesn't work, but you have to give it a go."

Analysts, however, see Farah temporarily ditching his marathon ambitions and returning to the track for the time being, perhaps seeking to defend his track titles in Rio in 2016.

"It is a disappointing debut," wrote Ross Tucker, a leading South African sports scientist who runs the influential sportsscientists.com website.

"What would be most concerning to Farah is that he ran pretty conservatively, and was on 2:06 pace for most of the race, and he still dropped substantially off that."

He said the result "probably signals a delay in Farah's marathon aspirations for a while. Back to the track for now, I would assume."

Distance running site LetsRun.com said Farah's performance "wasn't awful" and gave him credit for making his marathon debut in London, which had which arguably assembled the greatest field in men's marathon history.

But it also dismissed any chance of Farah ever being in contention for the race, and contrasted the performance with that of Ethiopian legend Kenenisa Bekele -- whose 2:05:03 debut in Paris the previous weekend, a course record, sets him apart as a 10,000m champion who has made the succesful leap to the marathon distance.