His Garmin-Sharp team says he suffered the injury in a crash during the race's first stage over the weekend.
Hesjedal says he had been uncomfortable since the accident and an X-ray confirmed the fracture Wednesday.
"A lot of times with rib injuries fractures don't show up right away so waiting until today we were able to confirm what's going on," Hesjedal said in a statement. "There's not much you can do about a fractured rib except for deal with the discomfort so that is what I've been doing and will keep doing."
The broken rib comes after Hesjedal was forced to withdraw from the Tour de Suisse last month due to injuries suffered in a crash. In May, he pulled out of the Giro d'Italia — a race he won in 2012 — due to illness.
Hesjedal's teammate Christian Vande Velde crashed in Stage 5 Wednesday.
"Ryder and Tom are both OK, so we're happy about that," said Garmin-Sharp director sportif Charly Wegelius. "We'll need to see how Christian does tonight and we'll make the call in the morning on whether or not he can start."
The team doctor said tests showed a blood clot in Vande Velde's neck muscle and a loosened screw — from a previous injury — in his clavicle plate.
"From what we can tell, it is possible that the screw may have jabbed a muscle," said Prentice Steffen. "Preliminary X-rays do not show a fracture but it probably flexed a bit in the crash and disrupted a screw."