World 100m champion Tyson Gay and record-holder Asafa Powell claim they are not allowed to face each other at the Golden Grand Prix in China.
Powell (right) congratulates Gay after his World Championship win
Gay competes in the 100m in Shanghai on Friday, while Powell runs in the 200m.
Powell, 24, said: "I wanted to run the 100m but I wasn't allowed to. I don't know why, you should ask my manager."
Gay, 25, added: "Asafa wants to run the 100m, I don't really know what's going on. Maybe someone wants to see the big match-up in Beijing [at the Olympics]."
Gay and Powell have only faced each other once this year, when the American produced a storming finish to win the World Championships in Osaka in 9.85 seconds on 26 August.
There's very little for Tyson to gain and a lot to lose - I'm not sure about his motivation to face Asafa
Powell's manager Paul Doyle
Powell, who admitted giving up when he knew he could not win and ended up finishing third, responded by setting a new world 100m record in 9.74 seconds 14 days later in Rieti, Italy.
Powell wants to gain revenge on Gay for defeat last month, but said: "At first when I heard, I kept asking my manager why I was running the 200.
"They know I don't like the 200 because it hurts afterwards. I wanted to run the 100 but they said run the 200, so that's what I have to do."
Powell's manager Paul Doyle said Gay did not want to face Powell so soon after his victory in Osaka.
"When these athletes match up they need to be 100% and I think Tyson is not ready at this stage of the season to race Asafa," said Doyle.
"If I was in his shoes, I wouldn't want to race either - there's very little for him to gain and a lot for him to lose.
"We realise the world wants to see this race. I know Asafa is hungry to race Tyson and make up for his loss in Osaka.
"The only thing I'm not sure about is Tyson's motivation to race Asafa."
Gay said he was "excited" about Powell's new record, set on 9 September, and admitted he coveted the tag of world's fastest man.
"The gold medal is very important to me but right now Asafa Powell is the fastest man that ever walked the earth. That's a great privilege to have," said Gay.
Powell believes the record is his proudest achievement.
"I'd love to have a gold medal but I wouldn't give up my record for anything you could give me - anything else in the world," he said.
Friday's Golden Grand Prix kicks off a mini-Asian tour with many of the world's top athletes also visiting Yokohama in Japan on Sunday and South Korea's Daegu on Wednesday.