At his height, Lomu was one of the most feared players in the world

The 31-year-old, who won 73 All Black caps, had a kidney transplant in 2004 but recently had a spell with Cardiff.

Lomu was offered a one-year deal by the Titans but has opted to stay in union.

"We understand and respect the decision Jonah has made and wish him all the best in rugby and in life," said Titans chief executive Michael Searle.

"Both Jonah and his wife Fiona have been a pleasure to deal with and we look forward to having them as guests of the Titans at an NRL game in the near future."

The Titans have already signed up Wallaby union international Mat Rogers for the 2008 season.

Lomu made his comeback in 2005 after his debilitating kidney illness, but any hopes of regaining a place in the All Blacks squad ended when he failed to win a contract with any of New Zealand's five teams for the 2007 Super 14 season.