Lewis Hamilton has withdrawn from Mercedes' tyre test in Barcelona in order to rest a niggling foot injury ahead of next weekend's US Grand Prix in Austin.
The defending World Champion aggravated his foot in training on Tuesday and was replaced by teammate Nico Rosberg for today's testing, with reserve driver Pascal Wehrlein taking Thursday's session.
The testing of Pirelli's 2017 tyres would've been Hamilton's first mid-season testing run since the 2014 season, and despite his withdrawal, Mercedes say his participation in next week's race is not under threat.
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A team spokesman commented on the matter: "Lewis had some discomfort in his foot after training on Tuesday.
"It was agreed he wouldn't test so he could rest it and get physio to be in good shape for Austin, which he will be. No concerns on that front."
Rosberg, who leads Hamilton by 33 points heading in to the US Grand Prix, completed 60 laps in Barcelona in a modified version of last season's car to test the new wider tyres ahead of next season.
However, the session was later hit by rain, which meant testing became difficult.
Three-time World Champion Hamilton is coming off a difficult week in Japan, in which he dropped further points to his teammate in the battle for the drivers title, and was also involved in controversy with the media after playing around on Snapchat during a press conference.
He then refused to answer questions after the race, describing the media as 'disrespectful'.
An awful start to last weekend's race allowed Rosberg to coast to victory and the Brit now desperately needs a win in Austin to gain some ground back on the German.
His record in America is a good one though, with two wins in the last two races there.
The 31-year-old realistically needs to win every race from here on out and hope that his teammate falters in dramatic style if he is to have any chance of making it three straight world titles.