AFP - Australia's Casey Stoner, who has been treated for anaemia, has a date with 'The Doctor' Valentino Rossi on Sunday, but is unlikely to find the world champion in sympathetic mood.

Halfway through the 2009 season, Rossi has a nine-point lead over Yamaha teammate Jorge Lorenzo and is 16 ahead of 2007 world champion Stoner on a Ducati.

The 23-year-old Stoner felt unwell at the recent Catalonian and Dutch races and received treatment after the last round at Laguna Seca.

"It's strange and hard to understand," the Australian said. "I felt OK between the Catalonia and Dutch Grand Prix but during the race I felt sick again.

"To be honest I was never feeling 100 percent. At Barcelona I had stomach cramps and at Assen I threw up after the race. They are different symptoms but maybe they originate from a single problem."

Dani Pedrosa won in California to move into fourth place in the championship table.

The young Catalan is hoping for a good ride on Sunday if only to forget about last year's fall which occurred as he seemed set for victory on the rain-soacked track.

Memories of the rain in 2008 also linger in the mind of six-time Moto GP champion Rossi although a second place finish helped him turn the tide in the title race.

"Sachsenring isn’t one of my favourite tracks but I’ve had some great races there and generally it suits Yamaha well, which is good," said the Italian

"Last year there was a lot of rain in Germany but in fact we were able to take a great second place. I hope this year we can go one better."

Young Spaniard Lorenzo is battling a series of injuries stemming from his qualifying crash in California.

He suffered a collarbone injury, a small fracture in his right foot and two bruised ankles.

The 22-year-old said: "This is one of the circuits where I’ve never done particularly well, in fact I’ve only had one podium there, in 2006 when I was third in 250cc.

"Last year it rained a lot and unfortunately I fell on the third lap, so it wasn’t a weekend to remember but I hope this one will be very different."