Australian-born Liberal senator Zed Seselja has confirmed he is an Australian citizen with the right to serve in the parliament after checking with his Croatian parents.

The senator said he was prompted to phone home on Tuesday when his senate colleague Matt Canavan revealed he was stepping down from his cabinet position due to his dual citizenship.

“I certainly checked with my parents overnight as to whether they'd put in any application forms that I may not be aware of, and they certainly hadn't,” he told SBS World News.

“I think the rules in Croatia, the place of my parent’s birth, are that you have to apply, you have to show that you can speak, read and write Croatian, you have to live in Croatia for a period of time.”

“There're no issues in relation to my citizenship,” he said.

Senator Canavan alleges he was made an Italian citizen without his knowledge or consent when his mother filled out the paperwork in 2006.

Senator Canavan has stepped down from his position as a minister in the Turnbull government but is not quitting the senate, unlike the two Greens senators, Scott Ludlam and Larissa Waters, who resigned over dual citizenship in the past fortnight.

The case has been referred to the High Court, which will decide on whether Mr Canavan’s dual citizenship puts him in breach of section 44 of the Constitution.

“While I knew that my mother had become an Italian citizen, I had no knowledge that I myself had become an Italian citizen, nor had I requested to become an Italian citizen,” he said on Tuesday.

Joyce: Canavan never signed the forms

Nationals leader Barnaby Joyce has defended his colleague, claiming he never signed any citizenship forms.

“This has happened without his consent. And he was 25 years old at the time,” Mr Joyce said.

“He never signed a form.”

Mr Joyce said while the Constitution was “black and white” on the illegality of dual citizenship for parliamentarians, Mr Canavan would dispute the legitimacy of the application that his mother made, allegedly without his consent.

“How can you be signed up for something you never signed up for? That you never knew about?” Mr Joyce said.

But the opposition leader Bill Shorten has cast doubt on Mr Canavan’s version of events.

“How does an adult become a citizen of another country without signing a form?” he said.

He described the situation as “very unusual” and called on the Italian consulate to release any documentation relating to the matter.