Heinz-Christian Strache's house was raided on Monday as part of a bribery investigation into the appointment of a far-right party official to a high-ranking position at Casinos Austria (Casag), according to media reports.
Strache stepped down as vice-chancellor and leader of the far-right Freedom Party (FPÖ) in May over the so-called "Ibiza-gate" affair, which also ended up bringing down Kurz and his coalition government.
The raid is not related to that scandal, but it court further hurt Kurz's People's Party (ÖVP) in the September 29th polls.
The ÖVP has been widely expected to once again emerge as the single strongest party, but is still expected to need a coalition partner to reach an absolute majority in parliament.
In the latest investigation, prosecutors are probing whether a company appointment was made in return for the promise of granting gambling licences, a spokesman for the Public Prosecutor's Office against Corruption said.
Several raids have been conducted, he said.
Austrian media named Strache among those involved. The Standard daily reported the ÖVP had signed off on the appointment of the FPÖ official to the casino developer and manager.
There was no immediate comment from either Strache or Kurz. The FPÖ distanced itself from the probe, saying it hoped for a speedy investigation.
"The new party leadership, and the FPÖ are not connected to this in any way," the party said in a statement.
Strache, who is still an FPÖ member but no longer holds any party functions, is already under investigation over hidden camera recordings that were made on the resort island of Ibiza in 2017.
Those showed him appearing to offer public contracts in return for campaign help to a fake Russian backer.
Thomas Drozda of the Social Democrats (SPÖ) called on Austrians to not vote ÖVP or FPÖ in the election, saying the latest probe showed that "selling Austria apparently was part of the daily routine" when the two parties ruled.