Izzard, 50, started the endeavor as a tribute to anti-apartheid activist and former South African President Nelson Mandela, who spent 27 years in prison. The star's attempt to retrace the geography of Mandela's life in South Africa is being filmed for a documentary, the BBC reported.
"I set out to run 27 marathons in 27 days as a tribute to Nelson Mandela and his 27 years spent in prison," Izzard wrote on Facebook Thursday.
"Having completed 4 marathons, unfortunately, I have had to put my attempt on hold due to unforeseen medical complications that have arisen due to a multitude of factors including severe terrain, humidity and altitude," he said. "But I wish to say that my attempt is not over and I will return to South Africa and run the 27 marathons and finish this story. I owe that to Nelson Mandela who has inspired the world to struggle and succeed no matter what obstacles are thrown at us."
Izzard ran 43 marathons in 51 days in 2009 to raise money for Sport Relief, an offshoot of the charity Comic Relief, the BBC said.
The actor starred in the FX series "The Riches," as well as the films "Ocean's 12," "My Super Ex-Girlfriend" and "Valkyrie."