The 49-year-old comedian announced his decision in a lengthy statement, explaining that the effects of open-heart surgery two years ago have left him struggling to keep up with the show's gruelling schedule.
"Although I believed I was fit enough to take on Strictly and its demanding schedule, it became clear that I had bitten off way more than I could chew for this stage in my recovery," he said. "I had begun to feel symptoms that led me to seek an urgent consultation with my heart specialist, and it was her view that it would be better for the sake of my health to step back from the show.
"I'm proud of the three dances that Dianne Buswell and I managed to perform and deeply regret having to let her down like this. I couldn't have wished for a more talented partner or more patient teacher, and it's a measure of Dianne's professionalism and kindness that I was able to get as far as I did.
"Thanks too to everyone at home who voted for us. It was always going to be a difficult mountain to climb (for one thing it's made of glitter so it's very skiddy) and I've been especially touched by the support from fellow heart patients. I think perhaps I was too eager to impress them. They will know that recovery doesn't always go in a straight line, and I hope they're not too disappointed that I ran into the limits of my resilience much sooner than I'd hoped."
Sarah James, Strictly's exec producer, added: "Although we are so sad that Robert has withdrawn from the show we completely understand and support his decision, health always comes first.
"Despite their Strictly journey coming to an end earlier than anyone would have hoped, Robert and Dianne really made their mark on the competition, with three unforgettable dances choreographed superbly by the brilliant Dianne. They have been a wonderful partnership and we'd like to thank them for the commitment, creativity and joy they brought to the show.
"Everyone involved in Strictly Come Dancing sends Robert their love and best wishes for his continued recovery."
The BBC confirmed that the 12 remaining couples will take to the dancefloor this weekend, suggesting that Webb may not be replaced by a backup contestant. body check tags ::