National's Botany MP Jami-Lee Ross will take a few months off from Parliament to deal with some "personal health issues".

"There are times in life where you have to put your own health and family first. As a husband and a father I need to do that at this time," he said in a statement this morning.

"That is why I have asked to have some time off on medical leave for a few months."

In a separate statement, National Leader Simon Bridges said the decision was "unrelated to the ongoing leak investigation."

Bridges' travel expenses were leaked to media earlier this year.

Lee-Ross said Bridges had been "very understanding and agreed to this along with my request that my transport and infrastructure portfolios be reallocated and that I step back from my front bench role".

"I look forward to returning to Parliament in the future to re-join our caucus."

His transport portfolio will be picked up by Paul Goldsmith and his infrastructure responsibilities by Judith Collins. Paul Goldsmith's revenue portfolio will be picked up by Andrew Bayly, Bridges said.