Rand Paul said on Wednesday that he's not sure if his Canadian-born rival for the Republican presidential nomination Ted Cruz is eligible to be president of the United States.

"You know, I think without question he is qualified and would make the cut to be prime minister of Canada, absolutely without question, he is qualified and he meets the qualifications," the Kentucky senator said of Cruz on the radio show Kilmeade and Friends.

In an interview with the Washington Post on Tuesday, Donald Trump said Ted Cruz' Canadian birth would be a "big problem" for the Republican Party.

Asked again if he thought Cruz was qualified to be president, Paul said he wasn't "an expert" on what the Constitution says about natural-born citizens.

"You know, I'm not an expert on the natural-born clause in the Constitution and people have various opinions," said Paul. "Some people believe it means you need to be born here, some people think it means you can be born in another country as long as your parents are citizens."

"And we've had some previous cases of it, but I don't think we've ever gone through the court system for the Supreme Court to decide one way or another," he continued. "It is interesting, and I think sometimes people point out that it's a double standard, in the sense that people went out, hot and heavy, including Donald Trump you know, about President Obama when there was really nothing more than conjecture that he wasn't born in the country. And yet, there hasn't been really the same outrage at all for some one who actually is born in another country."

Paul seemed more certain of Cruz' eligibility in a 2013 interview with CNN, saying, "You won't find me questioning his eligibility. I decided a long time ago I wouldn't be a birther. I'm not a birther for Democrats. I'm not a birther for Republicans. I'm staying out of that."

Later in Wednesday's radio interview, Paul again said he didn't know how a court would decide on Cruz' eligibility.

"You know, we live in a really litigious world and it is a concern that people will sue over him not being born in the country, you know, it hadn't been a big discussion yet and I think this will begin the discussion of it," said Paul. "I am not enough of a legal scholar to say the court will decide one way or another. In fact, probably nobody knows how the court would decide because it's never been adjudicated before."