Team Sky rider Chris Froome has suffered a back injury, which has forced him to withdraw from the Tirreno-Adriatico.
The Tour de France champion has joint inflammation in the lower back, meaning that Richie Porte will take Froome's place as leader of the team.
Team Sky's Dr Alan Farrell said: "Chris has suffered a slight inflammation to the sacroiliac joint in the lower back. As a precaution we have chosen to withdraw him from next week's Tirreno-Adriatico so he can focus on recovering and preparing for the Volta a Catalunya."
Performance manager Rod Ellingworth added: "This is just a minor setback for Chris and we hope he will get back to full training within a week. He's obviously disappointed to miss Tirreno-Adriatico, but we shouldn't take any chances at this stage of the season."
Geraint Thomas will become team leader at Paris-Nice, while Ben Swift will ride Strade Bianche on Saturday, replacing Sir Bradley Wiggins.
