Earlier this month, the 32-year-old withdrew from the individual time trial for the Championships in Limburg, with British Cycling performance director Dave Brailsford saying: "To expect Brad to hold form is a big ask.
Cavendish sprints to World title
"Once again we find ourselves in a very fortunate position of having a strong pool of riders across the board. Brad has opted out of riding the time-trial at the worlds. This year's focus for him has been fully on the Tour de France and the Olympics."
Thomas, who was one of the men selected on the GB long-list for the time-trial and road race but not chosen to race in either, will compete for Team Sky in the team time trial, alongside the likes of fellow-Brit Dowsett and Norway's Edvald Boasson Hagen.
The team time trial is a new event at this year's World Championships and sees riders competing in the colours of their professional teams, instead of their countries.
Great Britain squad for the 2012 UCI Road World Championships:
Elite men - road race
Mark Cavendish, Steve Cummings, Alex Dowsett, Chris Froome, Luke Rowe, Ian Stannard, Ben Swift, Jonathan Tiernan-Locke, Bradley Wiggins
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