The Team Sky rider, who was making his first appearance in the Classics in 2018, lasted until the 160km to go mark in the race as he was one of a number to hit the deck on the mud-covered cobbles at Troisvilles.
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This was Thomas’s fifth attempt at Paris-Roubaix, with his best result coming in 2014 where he finished in seventh place as Niki Terpstra took the victory.
Team Sky confirmed that Thomas had crashed on the opening sector at Troisvilles, which pictures taken ahead of the race had shown was covered in mud in parts.
The crash took down around 10 riders and held up many more, with Oliver Naesen (Ag2r La Mondiale) and Greg Van Avermaet (BMC Racing) among those who had to work hard to regain contact with the main bunch.
Team Sky’s bad luck continued after the fourth cobbled sector at Quiévy, when Gianni Moscon hit the deck on the smooth tarmac going through a left-hand bend.
The team will provide an update on Thomas’s injuries later in the day, with the next race on the Welshman’s calendar being Liège-Bastogne-Liège on April 22.