The state's electoral commission, police and corruption watchdog have been asked by Labor to investigate after Matthew Guy's chief of staff Mitch Catlin requested the donor make the payments.
The contract sent to wealthy past donor Jonathan Munz, the founder of plumbing supplies company Reliance Worldwide Corporation, was not signed but Mr Catlin stood down on Tuesday after it came to light.
Invoking an excuse he has previously criticised the Labor government for using during its own integrity scandals, Mr Guy said he could not comment because authorities have been asked to investigate.
"I can't run a running commentary on a matter that they have sent off to every investigative body in this state bar the AFL tribunal," he told reporters on Thursday.
Mr Guy says it was not an attempt to dodge donation laws and does not know why it was sent to his personal email.
But Mr Guy has also declined to release all correspondence between him and Mr Catlin in the lead up to his hiring to back up his claims.
"Why would I put that to you to be a value judgement when the Labor party has referred it off to everyone under the sun."
Under Victorian law, political donations above $1050 must be disclosed and are capped at $4210 over four years for individuals and organisations.
The Victorian Electoral Commission has initiated preliminary inquiries into the allegations, saying it takes regulation of political donations very seriously.
Victoria Police confirmed it received Labor's referral and is assessing it, while the Independent Broad-based Anti-corruption Commission declined to comment.
Mr Guy said his new chief of staff would start soon and immediately begin working on a code of conduct for opposition staff before cutting the press conference short.
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