MotoGP legend Valentino Rossi celebrates his 39th birthday during day one of testing in Thailand today (Friday).

Rossi won the 125cc title in 1997 and 250cc title in 1999, before making his premier-class debut on a 500cc Honda the following year. Runner-up to Kenny Roberts in his rookie campaign, Rossi romped to the final 500cc crown in 2001 and was champion of the new four-stroke MotoGP in 2002 and 2003.

A switch to the struggling Yamaha factory in 2004 sensationally brought instant title success, before Rossi's five-year run was finally broken by Nicky Hayden in the 2006 Valencia showdown.

2007 saw a further defeat, at the hands of Casey Stoner and Ducati, before Rossi and Yamaha returned to the top in 2008 and 2009. A broken leg in 2010 was followed by an ill-fated move to Ducati and, after just three podiums in two seasons, he returned to Yamaha in 2013.

The Doctor has won ten races during his second chapter at Yamaha, finishing as title runner-up in 2014, 2015 and 2016. Chassis troubles and injuries left Rossi fifth in last year's standings, his lowest position as a Yamaha rider, but he was still able to celebrate victory at Assen alongside five further podiums.

Unlike team-mate Maverick Vinales, Rossi is yet to sign a new contract with Yamaha to confirm that he will race on beyond the end of this season. However, encouraging form since switching back to the 2016-style M1 chassis means Rossi is expected to sign a new contract by the early stages of the season.

"I said that I want to wait until after all the tests because first of all I want to understand if I am competitive, if the bike is competitive," Rossi said at last month's Sepang test. "And also it's the worst moment of the season, so if I have enough power to make the tests, I will re-sign [laughs]!

"I have motivation. I want to try to continue," he added. "The experience [with age] is important for sure. Physically you pay something [as you get older], but physical condition is not the most important thing."