Former Passenger Rail Agency of South Africa (Prasa) CEO Lucky Montana is set to testify before the parliamentary inquiry into state capture on Tuesday afternoon.
MPs will be keen to hear what he has to say about a meeting involving himself, deputy public enterprises minister Ben Martins, the president's son, Duduzane Zuma, and Rajesh "Tony" Gupta.
Martins has said he was introduced to the Guptas by Montana, but Montana has insisted it was the other way round.
Montana has also claimed he is "the only CEO in the country" who rejected the Guptas advances, specifically "to manipulate the R53-billion Prasa tender for new commuter trains".
He had not allowed this to happen, despite a leadership that "failed to protect me".
Montana was removed as Prasa CEO in 2015.
His appearance before the inquiry comes a day ahead of Martins, who will find himself in the hot seat on Wednesday morning.
Martins was due to appear late last year, but chose to send a letter to the public enterprises portfolio committee – which is conducting the probe – saying his attendance was not necessary.
He has now been convinced otherwise, following a threat by the committee to have him subpoenaed. Reports on Monday indicated that he will present himself to answer questions before MPs at 9.30am on Wednesday.
There are further reports that members of the Gupta family may appear before the inquiry in a month's time.
According to Fin24, quoting committee chair Zukiswa Rantho, this will take place on March 6.
Last week, the inquiry heard evidence from Eskom head of generation, Matshela Koko, and the power utility's former chief financial officer, Anoj Singh.