Special Investigating Unit (SIU) head Willie Hofmeyr is the latest crime fighter being probed, The Star reported on Monday.

The investigation was over procurement issues relating to the SIU, after its former chief financial officer, Veronica Marshsmit, was suspended and later resigned.

Hofmeyr on Sunday confirmed that he was under investigation, the report said.

Asked why he was being probed, Hofmeyr said: "It is to be expected that there will be efforts to discredit those dealing with serious corruption, and this has happened in the past. One just has to be tough enough to deal with it when it happens.

"At the same time we are all equal before the law and I cannot expect to be given special treatment. But I expect to be treated fairly."

The National Prosecuting Authority declined to comment on Sunday night, the report said.

The SIU is involved in several serious investigations, among them a probe into police procurement procedures.

In March Hofmeyr told MPs the SIU was probing 16 departments and public entities for fraud, graft and maladministration.

News of the investigation follows just days after claims that Public Protector Thuli Madonsela was facing a criminal probe.

Democratic Alliance justice spokesperson Debbie Schafer said there appeared to a "sinister" motive for investigating Hofmeyr and her party would monitor the probe carefully.

Schafer noted that Hofmeyr recently told Parliament's portfolio committee on justice that the SIU was investigating procurement irregularities on the part of the police.

"In this context, one cannot avoid the conclusion that there is a more sinister motive behind the police investigation into Willie Hofmeyr."

She said it seemed a case of "one too many" coincidences that both Hofmeyr and Public Protector Thuli Madonsela, who is about to release her final report on the police headquarters lease scandal, were reported to be investigated for procurement issues.

"Since the elimination of the Scorpions, the SIU and the public protector are in reality the only truly independent institutions that investigate high-level corruption. How ironic that they are now both the subject of police investigations."