Johannesburg, May 18 (Reuters): Former Grand Slam doubles tennis champion Bob Hewitt was sentenced to six years in prison by a South African court on Monday after being found guilty of two counts of rape and a charge of sexual assault of minors, local media reported.

The Australian-born Hewitt, 75, was found guilty of assaulting three under-age girls during his time coaching children in South Africa in the 1980s and 1990s.

Before sentencing, Hewitt pleaded with the court to take his poor health into consideration and said he had received anonymous threats warning of assault if he was put behind bars, Talk Radio 702 reported.

Hewitt also told the court that he had suffered a stroke in 2010 and a heart attack in 2011.

The court extended Hewitt's bail until Tuesday when his legal team will appeal the sentence, the radio reported.

Hewitt won nine Grand Slam doubles and six Grand Slam mixed doubles titles in the 1960s and 1970s.

He also reached the semifinals of the men's singles at the Australian Open three times, and won the Davis Cup with South Africa in 1974 after settling there.