Nicky Hayden said it was time to listen to doctors' advice after withdrawing from MotoGP's Italian Grand Prix due to continuing pain in his right wrist.
The American has been hampered by the wrist issue - a recurring legacy of his Aragon 2012 crash - in recent weeks, but hoped it would not be an issue in Italy following treatments including hyperbaric chamber sessions after the last race at Le Mans, in which he was taken out on lap one.
However he was only able to complete a handful of laps during Friday practice and then decided to pull out of the event just minutes before Saturday morning's final session. Hayden will now have surgery in Italy on Tuesday.
"My wrist isn't getting any better so as hard a decision as it is to take the best thing for me is to listen to the doctors and skip this race," said Hayden.
"We need to stop thinking about riding and start thinking about a plan for the operation next week and my subsequent recovery.
"Mugello is a fast and physical circuit at the best of times but with the pain and loss of strength in my right hand it was getting really difficult to brake properly and it was risky to continue."
Hayden said the timing of the wrist problem was particularly frustrating as he felt he was just making headway with his new team Aspar, which he joined this year after five seasons as a factory Ducati rider.
"It is a shame to miss any race but especially Mugello, a circuit I love. It's also a shame for the team because we are really starting to build something together and we are understanding how to make progress more quickly during the weekend," he said.
"My mechanics are working hard to make things easy for me and to give me the chance to get faster. I feel bad to miss this round, for the team and the sponsors."
In Hayden's absence, Hiroshi Aoyama will be Aspar's sole MotoGP rider at Mugello.