Bai scored 12 tries in 26 appearances for Bradford

The 34-year-old - who would have been the oldest player in Super League XII - signed a one-year contract extension in September but has changed his mind.

"I've had enough and I don't think my body will hold up next year," Bai told the Bradford Telegraph & Argus.

"I really wanted to win a Grand Final with Bradford but some things don't work out."

Bai joined the Bulls at the start of Super League XI after spending the previous two seasons with Leeds Rhinos, with whom he won the Grand Final in 2004.

The Papau New Guinea international also had a brief spell with Hull, but made his name playing for Melbourne Storm in Australia's NRL.

"I found it hard to get in for training every day this year if I'm honest," added Bai.

I want to finish while my body is still in one piece Marcus Bai

"I've given everything though. I didn't think anyone would pick me up when I left Leeds but Bradford did and I've really enjoyed it there.

"I want to finish while my body is still in one piece. I don't want to come back, play four games, get injured and miss the next 26.

"That wouldn't be fair on the fans and it would be a waste of money."

Bai's debut for the Bulls was marked by two tries against Wests Tigers in the World Club Challenge, his third success in the competition.

"It's a blow. He scores tries, creates opportunities and works hard," said Bulls coach Steve McNamara.

606 DEBATE: Give your thoughts on Bai's decision to retire

"We'll miss him but he's been honest with us. His wife's just had a baby and he didn't feel his body would stand another season.

"He's been fantastic both on and off the field.

"It does leave us in a tricky situation but we'll monitor things and see where we go from here. It's going to give somebody else an opportunity and we still have a very strong squad."