Former London Marathon winner Steve Jones expects Mo Farah to break his 29-year-old British record on Sunday.
Farah, Olympic and world champion at 5,000m and 10,000m, makes his full debut in London's 26.2-mile race.
Welshman Jones's mark has stood since 1985 when he set a time of two hours, seven minutes and 13 seconds to win the Chicago Marathon.
"I'd like to hang on to it for another 29 years but it's time to go," said Jones, 58.
"It's not an easy target but it's pretty soft compared to the world level right now."
While Jones expects Farah to claim his British record soon, he hopes winning the London Marathon remains the 31-year-old's priority.
"I'd be a little disappointed if that's what Mo is focusing on," said Jones.
"He should be focused on winning the race. He's got all the tools, he's done the training, he's got a great coach - it should be his race in the bag really.
"A lot can happen but if he keeps his head and stays out of trouble anything is possible."
Farah ran the first half of last year's event but faces four of the 10 fastest marathon runners in history this weekend.
The strong field includes reigning champion Tsegaye Kebede, world-record holder Wilson Kipsang, course-record holder Emmanuel Mutai and Olympic and world champion Stephen Kiprotich.
Farah collapsed after finishing second in the New York half-marathon last month.
The current world record is two hours, three minutes and 23 seconds.