Joice Mujuru, a former vice president of the country who is now leader of the National People's Party (NPP), and her supporters were pelted while on the campaign trail.
Zimbabwe is due to hold general elections before July -- the first polls since independence hero Robert Mugabe was ousted after 37 years in power. Mujuru is one of the prominent contenders.
Mujuru was hit on the cheek with a stone and later addressed a rally in the working class suburb of Glen Norah after she received medical treatment, her spokesman said.
they came out of the shops to cheer her," Jeffryson Chitando told AFP.
More From This Section
"She got out of her car and greeted the people, and that is when ZANU-PF (activists) started throwing stones."
He said 10 of her supporters were injured.
Police did not respond to phone calls from AFP about the incident.
Zimbabwe's new president, Emmerson Mnangagwa, who took office in November after a shock military takeover led to Mugabe's ouster, has promised to hold credible and violence- free election.
Mujuru, was Mugabe's vice president from 2004 until he abruptly fired her in 2014 and later expelled her from ZANU- PF.