Sam Chisholm has reportedly quit as Chairman of Macquarie Media Investments because of conflicts of interest.

It is understood Chisholm flagged his intention to resign when the John Singleton radio group, which owns 2GB and 2CH, announced it would lobby for a fourth tv network.

Mark Day, writing in The Australian, says this put him in potential conflict with Foxtel, where he is also Chairman, and Foxtel half owner, Telstra, where he is an influential board member.

Day says the decision to resign might have encouraged Singleton to make further board changes, with speculation that two other Macquarie directors, Gary Charney and George Buschman, would also leave.

Chisholm was overseas when Mark Carnegie, principal of financial advisory firm, Carnegie Wylie, and a shareholder in Macquarie Media, spoke about a fourth tv licence in an address to the ABA annual conference.

Chisholm apparently contacted Foxtel and Telstra officials to distance himself from Carnegie’s announcement, and to indicate he would resolve the looming conflicts of interest on his return to Australia.

His resignations were reportedly lodged this week. Carnegie is tipped as his likely successor. He already chairs Singleton’s publicly listed STW Communications.

Chisholm is one of the most influential players in Australian media. He was chief executive to Kerry Packer and Alan Bond, and the driving force in the success of Rupert Murdoch’s British BSkyB in the 90s.

He teamed up with Singleton in 2001, when he planned and negotiated Alan Jones’ move from 2UE to 2GB.