The Pulp Fiction star, a supporter of cancer charity One for the Boys, tweeted the snap to promote the organisation's new initiative #InTheNipOfTime, which encourages male social media users to post pictures of their own nipples to raise awareness of breast cancer in men.

"Checkin' myself before I wreck myself!!" he wrote in the caption. "Taken #InTheNipOfTime all in aid of @One4theBoys Get Ur (your) nips out (sic)! Your turn!"

Jackson also narrates an accompanying video for the campaign, which encourages men to feel their breasts for suspicious lumps.

"Now these are some breasts you'll want to check out. Yep, that's right. Men don't just get man boobs, they can get breast cancer too," he says. "So when you think about copping a feel, cop a feel of yourself. But don't be the strong, silent type. If unsure, say something."

Scottish rugby player Jim Hamilton also supported the campaign by sharing a topless 'selfie'.

Jackson has worked with the charity since 2013, and has hosted an annual men's fashion show to raise money and awareness for the cause.