Rossi and Stoner battle continues

MOTEGI, Japan - Italian motorcycling superstar Valentino Rossi warns it will only get tougher to stop rival Casey Stoner after he regained the world crown by pipping the defending champion.

The Yamaha ace, dubbed the Doctor for his cool and clinical planning and racing, credited the 22-year-old Australian as being perhaps the toughest opponent he has ever battled.

"I think Stoner next year will be back stronger again," Rossi, 29, said as he wrapped up his sixth premier-class title, and the first in three years, at the Japanese Grand Prix here on Sunday.

"So maybe he is the hardest rival I have ever had, more than (Sete) Gibernau and all the others I fought against in the past. "Gibernau was the main challenger for Rossi's crown until 2005. The Spanish firebrand retired when Stoner replaced him at Ducati for 2007. It was at Motegi that Stoner crushed Rossi's hopes.