Ward said he is unable to even exercise without ‘irritating his symptoms’.
He missed the whole of the 2020 season after suffering a concussion in the Rhinos’ opening game of the year.
The club stood him down “indefinitely” in February, with head coach Richard Agar saying at the time it was “concerning”.
Ward’s contract with Leeds, who were the only team he played for in his career, expired at the end of 2020.
He made 109 Super League appearances and won two Grand Finals and one Challenge Cup
Ward said in a statement: “I have come to the conclusion, after over 11 months of severe symptoms, that I need to give this injury the respect and time it deserves and cannot put my health and brain to any further risk and detriment.
“On a daily basis, I struggle with migraines, dizziness, motion sickness, sensitivity to light and screens, short-term memory issues, slurred speech, and an inability to exercise or do daily tasks without irritating my symptoms.
“I love the game of rugby league. I am immensely proud to have competed on some of the biggest stages next to childhood heroes and test myself to the absolute limit while feeling the incredible buzz from the Leeds fans after being one myself as a youngster.”
In his statement, Ward revealed that he initially suffered a concussion in the pre-season friendly with Wigan last January before suffering a second against Hull FC in the Super League season opener a fortnight later.