The former NSW and Australian test captain called an end to his stellar career following hours of talks with leading spinal specialist Professor John Yeo today.
Johns, 32, underwent CAT scans this morning after aggravating a previous neck injury at training last Thursday in a collision with Newcastleteammates Daniel Abraham and Adam Woolnough.
"I'm still in shock," said Johns of his decision.
"I was in shock when it happened, just totally numb.
"It was really tough telling my family.
"I made an emotional call to my brother Matthew and it was even tougher talking to the players this afternoon.
"I think the time's right."
Newcastle captain Johns labelled his two premierships won with the Knights in 1997 and 2001 as the standout moments of his career, which began with his National Rugby League (NRL) debut against Gold Coast at Seagulls Stadium in 1993.
He played 23 State of Origin games for NSW and represented Australia in 21 test matches, including the 1995 World Cup and the 2001 Kangaroo tour.
Johns ends his career as the greatest pointscorer in NRL history with 2176 points from 249 first grade games with the Knights.
Johns was set to play for the All Golds on their centenary tour of Britain later this year which is essentially a Kiwis team.
Johns was originally eligible to play as their invitation player under the same rules as a century ago.
