Former Hour Record holder Dennis, 25, has been withdrawn from the prestigious French stage (March 6-13) after being diagnosed with sinusitis. Time trial specialist Dennis was one of the favourites to win the 6.1km opening prologue in Conflans-Sainte-Honorine.
"I really wanted to win the time trial on Sunday so it is disappointing to not be lining up," said Australian time trial champion Dennis.
"I’ve felt the illness lingering a bit in the past few days but today it has really hit me and we don’t have enough days ahead of Sunday for a proper recovery. At the end of the day my health is the priority and I’m focused on recovering well and lining up at my next race."
BMC Racing team doctor Daniele Zaccaria said: "Rohan is suffering from sinusitis, and although it is nothing too serious he will not be fit to race at Paris-Nice.
"His condition worsened this morning and given we are only two days out from the opening prologue, there is not enough time for him to fully recover, especially considering we are expecting cold weather and rain in Paris."
Watch: Secrets of the toolbox - BMC
Dennis will be replaced in BMC's line-up by Slovak Peter Velits. The squad's Richie Porte goes into the race as defending champion and leading overall contender. Porte moved to BMC from Sky for the 2016 season and will face former team-mate Geraint Thomas, as well as Alberto Contador (Tinkoff) and Tom Dumoulin (Giant-Alpecin).
Dennis enjoyed a successful 2015 season, winning the Tour Down Under overall in January and then going on to win the opening time trial stage of the Tour de France. He also won the USA Pro Cycling Challenge overall.
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