Hayden: The boot wasn't going on the foot.

Nicky Hayden was forced to abort a return to MotoGP race action on Sunday at Misano, after the heel injury that caused him to miss the previous Brno round got steadily worse during the San Marino Grand Prix weekend.

The 2006 MotoGP world champion broke two bones in his right heel when he made a heavy landing during practice for the X Games Supermoto event, in Los Angeles on August 1.

Hayden had made a determined effort to regain fitness as soon as possible - his treatment including bone stimulator, laser and ultrasound therapy - and kept pressure off the heel by using crutches or a walking stick.

Unfortunately, riding at Misano made the injury worse, and Hayden slipped from sixth in first practice to 16th in qualifying, before withdrawing from the event on Sunday morning.

"This wasn't an easy decision," said Hayden. "I love to race and the racer in me wanted to race, but in this kind of situation it's better to listen to the experts. The heel got worse as the weekend went on. I was sixth on Friday morning but I kept working my way backward after that, the more I rode, the more strength I lost in the foot.

"When I woke up this [Sunday] morning I had a lot of swelling and bruising, there wasn't any way the foot was going to fit in a boot," he revealed. "The team and I took the decision to try and be smart, to try to let it heal as best it can to get it ready for Indy, which is a huge race for me. I felt I could have salvaged a little something out of today's race but that was just going to make things worse for Indy and for the rest of the season."

"We believe Nicky made the correct decision not to ride and we fully support his decision," said team manager Kazuhiko Yamano. "Nicky is a real racer, so he very much wanted to race here. But it is better for him to be in a better situation for the final five races, rather than to race here and do further damage to the heel."

Whilst team-mate Dani Pedrosa will make his shock Bridgestone debut during testing on Monday, Hayden - who is staying on Michelin tyres - will fly to the US to continue treatment ahead of the Indianapolis Grand Prix on September 12-14.