Lord Coe is the right man to lead a clean-up of athletics, says Olympic medallist Brendan Foster.
Foster's support comes on the day a World Anti-Doping Agency (Wada) independent report is set to criticise governing body the IAAF, which Coe now heads, for failing to tackle doping.
Foster, now part of the BBC commentary team, said: "This is the worst day in the history of this great sport.
"The agenda is clearly set that he has to change the future of athletics."
Former Wada president Dick Pound last year released a damning report that was critical of the IAAF and led to Russian athletes being banned from competition.
He will issue the second part of that report on Thursday.
Foster, who won European 5,000m gold in 1974, added: "The sport, today, will be unveiled as clearly unable to be governed by the regime that was in place before Seb Coe was appointed.
"We've got a governing body that is not fit for purpose."
Foster has recently spoken to his fellow Briton and said the two-time Olympic champion was "hurting".
He added: "He is determined like no-one else can be determined. He's going to change this thing."
Lord Coe, 59, succeeded Lamine Diack as IAAF president in August, after eight years as a vice-president.
Foster, 68, believes the governing body needs to change its name and move from its headquarters in Monaco.
He also agrees with UK Athletics' proposal to reset world records to help achieve a "new era" of clean competition.
Foster said: "My view is 'park' that record book and start a new one."
Meanwhile, sports lawyer Gregory Ioannidis expects the second part of the independent Wada report to be "very damaging" to the IAAF.
Ioannidis, who has represented accused athletes, said: "The first part of the report focused basically on allegations of anti-doping violations on behalf of a specific country.
"The second part of the report I expect to perhaps focus on allegations of violations on behalf of IAAF officials.
"Obviously, I'm expecting this to be a very dark day for world athletics."