At the 1996 Atlanta Games, Johnson became the first man to win both the 200 and 400.
“Obviously, the primary goal has to be winning a (single) gold medal,” he told The Associated Press. “She hasn't done that yet.”
Felix is a three-time world champion at 200 meters, but at the last two Olympics, she's finished second in the 200 to Veronica Campbell-Brown of Jamaica. Felix has one gold medal in the 4x400-meter Olympic relay.
She has been talking about doubling in London and has signed up for all three sprints—the 100, 200 and 400 -- for the U.S. Olympic trials which begin on Friday. But she hasn't stated which events she'll run in Eugene.
At the Olympics, the 400 comes first on the schedule, followed by the 200, meaning anyone running in both faces six straight days of competition.
The IOC changed the schedule to accommodate a 200-400 men's double in 1996, which enabled Johnson to try to win gold medals in both.
Wearing his famous gold shoes, Johnson did, in fact, win both. He also set a world record in the 200. His mark of 19.32 seconds stood until 2008, when Usain Bolt beat it in Beijing.
Felix began training in earnest for a 200-400 double about a year ago. She tried for the double at the world championships last year and ended up with disappointing results: Third in the 200 and second in the 400.
“Last year was the first time attempting the double for her,” Johnson said. “That was eight years into her career. I'd have attempted something like that many, many years before that, learned from it and created a strategy from a competition standpoint that lent itself to eventually being successful at the double.”
Johnson, who believes Felix would be the world's best in the 400 if it was her sole focus, said he wasn't privy to her strategy and that nobody from her camp had asked him for any advice.
Last month, she conceded that training for both events was taxing.
“Sometimes you can spread yourself too thin,” she said. “For me this year, I just said, ‘OK, the 200 is my main focus.' If I do another event, it's going to come second to that.”
During the same news conference, however, Felix conceded the possibility of a less-taxing 100-200 double. She was coming off a personal best time of 10.92 seconds in the 100.
Johnson, who is promoting an Olympics-related app on Facebook, suggests Felix be mindful of an old saying—one he was reminded of many times back when he was trying for the double. Sometimes, when you try to win two gold medals, you end up winning none.
“Honestly, at this point, she should focus on 200 meters and try to win that gold,” he said.