“Sadly, I won't be able to compete at Il Lombardia on Sunday," he confirmed on the Sky team's website.
“I had some back pain at the World Championships last weekend and it hasn’t settled down as I'd hoped."
Team Sky Doctor Alan Farrell added: “A scan this week revealed that Chris is suffering from an inflamed sacroiliac joint. We are monitoring him as a team but unfortunately the injury means he will not be able to take part in the race this weekend.”
Froome pulled out of the World Championships road race last week.