Whitfield, who was diagnosed with non-Hodgkin's lymphoma in March, had been in remission until doctors recently advised him to resume aggressive treatment. Whitfield said at Comic-Con in July that he felt "better than ever" and was training hard to resume work on Season 2.
"It's with a deep sense of disappointment that I must step aside from such an exceptional project as Spartacus and all the wonderful people involved," Whitfield said in a statement. "It seems that it is time for myself and my family to embark on another extraordinary journey. Thank you sincerely for the support so far."
The epic drama halted production in March after Whitfield was initially diagnosed. The network then produced a six-part prequel to give Whitfield time to recover before starting work on Season 2. No immediate decisions have been made about the future of the series, but the prequel will still air in January 2011.
"Our hearts and prayers are with Andy and his family during this difficult time," Starz President and CEO Chris Albrecht said in a statement. "Andy is not only an incredible actor whose portrayal of Spartacus made an indelible impression on Starz audiences, he is also an amazing human being whose courage, strength, and grace in the face of adversity have inspired all of us."