The Ducati rider comes to the 10th of 14 meetings boosted by a win-double at Brno in the Czech Republic two weeks ago. That gives him a huge 79-point lead over Max Neukirchner, of Germany, with rival Australian Troy Corser a further 12 points back in third place.
Toseland said he would have jumped at the chance of competing this weekend, especially as he built up a great rapport with the crowds of over 100,000 who turn up for the annual superbike spectacular.
But he admitted he has his hands full coming to terms with the demands of riding a thoroughbred MotoGP Yamaha - in 11 races he has finished a highest of sixth four times to lie ninth in the world championship with 72 points, 140 points behind the pace-setting Valentino Rossi.
Toseland said: "It has been hard making the step up from superbikes, but I truly believe I can be as successful in MotoGP.
"What hasn't helped is my lack of experience. They're totally different bikes and I'm racing on eight tracks I've never been to before. But if everything comes together I know I can podium before the end of the season."
