Former Olympic champion Michael Johnson does not believe Usain Bolt can win gold in the 4x400m relay and defend the sprint titles he holds in London.
The Jamaican, 25, will defend the 100m, 200m and 4x100m titles in 2012.
Johnson says Bolt has the talent to break the 400m world record but should not overreach himself in one Games.
"You can't train for the 400 [as well], it would be an absolute distraction and the training wouldn't work," Johnson told BBC Radio 5 live.
Bolt has said he plans to run in the 4x400m relay as well as the shorter sprints and the 4x100m relay in a bid to emulate Carl Lewis's feat of four gold medals at a single Olympics.
Although there would be no schedule conflicts with the individual 100m event, the 4x400m relay heats take place on the same day as the 200m final (9 August).
The following day there is another potential clash with the opening rounds of the 4x100m, in which Bolt will attempt to help Jamaica defend the Olympic title they won three years ago.
Speaking after being named Athlete of the Year by world governing body the International Association of Athletics Federations (IAAF), Bolt insisted his Jamaican team-mates were improving in the 4x400m and that he wanted to help his country win the Olympic title for the first time since the 1952 Helsinki Games.
"If I can help to get them a gold medal, I will want to go on that team," said the three-time Olympic champion.
Johnson, who won gold in the 200m and 400m at the Atlanta Olympics in 1996 before retaining his 400m title in Sydney four years later, admits Bolt could succeed at the longer distance, but that he would be surprised if it became a reality.
"I think he could be the world-record holder at 400 metres but he's said that he has no interest in training for it, which I can understand - it's a difficult race to train for," said Johnson.
He added: "I see no reason why he shouldn't be able to repeat as an Olympic gold medallist in the 100m, 200m and the 4x100m, but the 4x400m is going to be tough.
"Without him the Jamaican team certainly doesn't have enough 400m runners to beat the United States - they could beat the US possibly with him on the team if he was training for the 400m, but he can't just step onto the track and run a 44 or a 43-second split just off 100 and 200m training.
"I don't see that happening. I don't see the Jamaican coaching staff putting him on the 4x400m relay unproven. That means he's got to go out there and run some 400s during the season, in order to prove that he should be on that relay.
"In order to go out and run some 400s, and run them fast enough, that means he's got to train for it, which is something he said he's never going to do."
You can hear the full interview with Michael Johnson on BBC Radio 5 live's London Calling programme with Eleanor Oldroyd on Thursday at 2100 GMT.