Clive Derby-Lewis sustained "minor" injuries on his back after another inmate attacked him yesterday with a piece of glass, said Manelisi Wolela, spokesman for the correctional services.
Derby-Lewis was treated at a prison clinic, Wolela said. Prisons authorities have launched an investigation into the assault.
Derby-Lewis and Janus Walusz, who was also jailed for Hani's murder, were on February 26 attacked with a spoon by a fellow prisoner. They suffered lacerations on their heads and hands.
The death of the charismatic and hugely popular leader came at a crucial point in political negotiations to end white minority apartheid rule, and many feared it would spark a civil war.
Also Read
The assassination pushed racial tensions to near-breaking point, prompting riots and deaths that prompted the late liberation hero Nelson Mandela to call for peace in a nationally televised address.
Mandela became South Africa's first black president following the first all-race elections a year later.