Marathon world record holder Kelvin Kiptum was a "special talent" who would gone on to have an "incredible career", says Sir Mo Farah.
Kiptum, 24, died in a car crash alongside his coach Gervais Hakizimana in his native Kenya on Sunday.
He broke Eliud Kipchoge's world record last year and was set to compete at this summer's Olympics in Paris.
"Kelvin was an amazingly talented athlete and had already achieved so much," Briton Farah said.
Farah, Britain's four-time Olympic champion over 5,000 and 10,000m, finished ninth in last year's London Marathon - a race Kiptum won in a record time of two hours, one minute and 25 seconds.
"He truly had a special talent and I have no doubt he would have gone on to have had an incredible career," Farah said.
"I send all my sympathies and condolences to his and Gervais' family and friends at this tragic time."
Kiptum also broke the record for fastest debut marathon in Valencia in 2022 before bettering Eliud Kipchoge's overall record in Chicago in October last year, clocking the 26.2 miles (42km) in two hours and 35 seconds.
Just last week, his team announced that he would attempt to become the first person to run the distance in less than two hours in open competition.
Britain's Emile Cairess, who finished sixth in London last year behind Kiptum, said the Kenyan could have become "Usain Bolt-esque" as a "figurehead of athletics".
"It's a massive blow because at his level, someone can really capture the attention of people outside off the sport," Cairess told the BBC.
"Many people thought they would never see a sub two-hour marathon in their lifetimes but since he came along, it's like it was just a given that he would do it because of his exceptional performances so far.
"It was almost certain that he would have done it. It's terribly sad and a real shame that we won't get to see him again or to attack that barrier."
Kipchoge, 39, completed a marathon in Vienna in one hour 59 minutes 40 seconds but that time does not count as an official record as it was in a specifically arranged sponsored event with pacemakers.
Kiptum's performances in the past two years had seen him emerge as a rival to his great Kenyan team-mate.
In paying tribute, Kipchoge said he was "deeply saddened by the tragic passing".
"[Kiptum was] an athlete who had a whole life ahead of him to achieve incredible greatness," he said.
"I offer my deepest condolences to his young family."
Sebastian Coe, the president of World Athletics, said Kiptum was "an incredible athlete leaving an incredible legacy".
"On behalf of all World Athletics, we send our deepest condolences to their families, friends, team mates and the Kenyan nation," Coe said.
Kiptum's road accident happened at about 23:00 local time (20:00 GMT) on Sunday, police were quoted as saying by the AFP news agency.
Giving further details of the crash, police said Kiptum was the driver, and the vehicle "lost control and rolled, killing the two on the spot".
A spokesman quoted by AFP added that a female passenger had been injured and "rushed to hospital".