1993 500cc world champion Kevin Schwantz is surprised and concerned at Casey Stoner's decision to sit out three rounds of this year's MotoGP World Championship - and thinks James Toseland is lacking the 'fire' he had in World Superbikes.

After an impressive opening five rounds, after which Stoner was leading the world championship with two race wins, the Australian struggled with sickness and then fatigue at the next five races.

Tests proved inconclusive and, after returning to Australia for further medical advice during the summer break, Ducati's 2007 world champion announced that he would miss the next three rounds to try and get back to full fitness.

"The doctors believe that during the Barcelona race [round six] I was suffering from a virus, and, that I subsequently pushed my body too hard, leading to problems that have caused my fatigue since then," Stoner stated. "The doctors are continuing with many tests to try to understand these problems and make sure it does not happen again."

But Schwantz, speaking during a media teleconference to promote next weekend's Indianapolis round of the MotoGP World Championship, thinks there may be other factors involved.

"And as a rider, my gut feeling is Casey needs to be out there competing," said Schwantz. "This championship, when he made a [wet] tyre choice at Donington that seemed to be a little bit off of the norm, had him right at the top of it.

"I mean, he didn't need to be making a gamble on tyres like that when he was in a championship hunt. For me, that kind of told me that there was something more going on with Casey than just, you know, 'I don't really feel all that good but I'm finding a way to perform.'

"And for me, to have signed a contract whenever it was, beginning of last year, beginning of this year, you're signing a contract to compete unless something is medically wrong with you. I'm out there doing the best that I can.

"Whether I can give 100 percent every weekend or not is kind of the question. But for me it's a real disappointment, and I think, you know, Casey is a great competitor, and I think maybe a little bit more of this has to do with something behind the scenes that maybe none of us quite yet know about.

"Maybe that's just some Stoner hard feelings towards Ducati or towards the series or, I don't exactly know what it could be. But to just decide you're going to skip three races and see if you feel any better at the end of it, to me, is a little bit out of the norm," Schwantz stated.

After many years battling arch-rival Wayne Rainey, Schwantz found his own motivation disappear after his fellow American suffered a career-ending injury during the '93 season. Schwantz quit grand prix racing three races into the 1995 season.

"When I quit racing, it was... any motivation, any focus that I had had, any inspiration to go out there and compete every weekend was a lot, was based around trying to figure out how to beat Wayne Rainey," Schwantz confirmed. "Without Wayne there, winning a race is winning a race; and it was still really cool, but it didn't have near the meaning that it did when I was beating him.

"If your heart is not in it, it's somewhat of a high-risk profession. Maybe you're better off going to go get a desk job or at least stepping away from the sport. And that, in my situation, is what I did.

"I sure hope that's not the case with Casey Stoner and that [he hasn't] lost interest and focus in this sport at such a young age because he's definitely a huge draw to the series. He's been a world champ, so he obviously can ride one of these two-wheel rockets at the best of his ability, which is world championship-winning level."

Meanwhile, another former world champion, in World Superbike, is facing different difficulties in MotoGP this year.

James Toseland, who won the WSBK crown for Ducati and Honda, has experienced a tough second season in grand prix racing - scoring ten points less than at the same time last year and is still to beat his best race result during his rookie season (sixth).

While team-mate Colin Edwards is fifth in the championship and the leading satellite rider, Toseland is just 13th and under pressure to perform if he is to keep his Tech 3 seat for 2010.

"I think James has been as disappointing to us as he has been to himself," said Schwantz. "I know James probably didn't expect to come here and start winning races immediately, but I'm sure he felt like he was going to be a guy that could contend for the podium.

"When you've got a veteran such as Colin Edwards alongside you in the team who's managing to put the bike up on the podium or somewhere right near the front somewhat consistently, I think there's probably a lot of doubt running around in James' head right now.

"I don't know, maybe a year or two back ride some superbikes, get some confidence back. I don't honestly know what the best path might be right now for James. But I know for me it's - I was expecting big things of him and he's done an OK job a couple of weekends.

"He's had some decent results, but he hasn't ever shown me that spark and that fire that I saw out of him riding a World Superbike."