Economist Thabi Leoka has resigned from her directorship at Anglo American Platinum as questions about her PhD show no sign of abating.

In a note to shareholders, Amplats said Leoka had resigned with immediate effect to "attend to her health and the questions she has been facing in relation to her academic qualifications".

For the past week, Leoka has been facing questions about whether she received a PhD in economics and economic history in 2008 from the London School of Economics. 

While the 44-year-old maintains she was awarded the degree, the university has said it can find no evidence of it.

Leoka, who is currently in the US undergoing medical treatment for glaucoma, remains on the boards of two companies: MTN SA, and the Small Business Institute. 

MTN SA told News24 last week that it had been in contact with Leoka and was "reviewing its own internal processes" related to her onboarding in 2018.