South African businessman Mathews Phosa said he accepted a nomination to stand as president of the ruling African National Congress.

Phosa will challenge Deputy President Cyril Ramaphosa and Nkosazana Dlamini-Zuma, a former chairwoman of the African Union Commission, who are seen as the frontrunners to succeed President Jacob Zuma as the party’s leader at a conference in December. Dlamini-Zuma is the president’s ex-wife.

Zuma is under pressure after S&P Global Ratings and Fitch Ratings Ltd. responded to his firing of Finance Minister Pravin Gordhan last month by cutting their assessments of South Africa’s international credit to junk. There have been growing calls for him to step down, and he faces a vote of no confidence in parliament that’s been postponed pending a court ruling.

“I think my movement is in a crisis, my country is in a crisis,” Phosa said by mobile phone on Sunday.

A lawyer, Phosa is a director at coal and platinum companies, and was previously treasurer general at the ANC. He was nominated by the ANC ward in Cape Town. The leader of the party will stand in the country’s general elections scheduled for 2019, with Zuma having served the maximum two terms allowed under the constitution.