According to his team, Porte fell ill after the Portuguese race, which finished on February 18, forcing him to miss a week of training ahead of one of the biggest races of his spring calendar.
"Richie Porte developed an upper respiratory infection after Volta ao Algarve which forced him to miss the best part of a week's training, said Dr Max Testa, BMC Racing's chief medical officer.
"Given Tirreno-Adriatico was one of Richie's goal races this season, it did not make sense to line up when his preparation was far from ideal.
"Richie and the BMC Racing Team management and medical team agreed that it was in his best interests to miss Tirreno-Adriatico and adjust his race program, in order to recover properly."
After Tirreno-Adriatico, Porte was not scheduled to race again until the Tour du Finestère in mid-April, however his withdrawal from Tirreno-Adriatico could see him tempted by another week-long stage race, such as the Volta a Catalunya, which starts in eastern Spain on March 25.
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"I'm looking forward to going back to Tirreno-Adriatico next week," Dennis said. "One main goal of the team will be to win the opening team time trial again, and we are motivated to do that. For me, the individual time trial will, of course, be another target and I hope to repeat my success from last year. In between the two, we will see what happens.
Even without Porte, the Tirreno-Adriatico start list is still packed full of major GC riders, all looking to use the week-long race to continue their build up towards the season's Grand Tours.
Among those on the start list will be Chris Froome (Team Sky), Romain Bardet (Ag2r La Mondiale), and Vincenzo Nibali (Bahrain-Merida), while the likes of Peter Sagan (Bora-Hansgrohe) and Fernando Gaviria (Quick-Step Floors) will be using the event as preparation for Milan-San Remo.
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