Canberra cycling star Michael Matthews' run of bad luck continued with a crash ruining his chances of winning the Clasica San Sebastian in Spain on Sunday.

Illness forced Matthews out of the Tour de France, where he was defending the green jersey he won in 2017, and he was hoping to put that behind him with victory in the one-day race.

A crash 20 kilometres out from the finish, while not injuring Matthews or his Sunweb teammates, forced them to change bikes and wheels and ending their hopes of being involved in the finish.

Quick-Step Floors' Julian Alaphilippe took out the race, with Trek Segafredo's Bauke Mollema finishing second.

Matthews finished 55th, more than five minutes off the pace.