Jarryd Hayne has taken a massive step towards his dream of playing in the NFL, linking with the San Francisco 49ers.

Hayne left the Eels last October with hopes of playing in the NFL and, at a press conference in Sydney on Tuesday, he announced he has signed on to train with the 49ers ahead of the 2015 season, starting in September.

The former Parramatta, New South Wales and Australia star thanked the Seattle Seahawks and Detroit Lions for their interest, before announcing he would be a San Francisco 49er in 2015.

The Lions initially shaped as the front-runners, but the 27-year-old said he agreed to a rookie contract with the 49ers.

The deal is worth $US100,000 and guarantees him a spot at the club for 15-20 weeks.

Hayne said when his agent first suggested going to San Francisco, he said no, because of the turmoil surrounding then-head coach Jim Harbaugh.

Harbaugh eventually left the club and was replaced by Jim Tomsula, with whom Hayne had previously had a meeting.

Tomsula had experience as a coach in NFL Europe, dealing with the transition of rugby players into American footballers.

"When he became head coach, I rang my agent back and said 'the one guy I spent the most time with is the new head coach'," he said.

Hayne said the 49ers had made a "serious offer" two weeks ago, and that he had told the team last Friday he was accepting the offer.

"I spoke to (49ers general manager) Trent Baalke and we did the handshake over the phone," he said.

"It feels surreal to me, it's a small step in the right direction. The hard stuff starts now."

"A lot of boys are interested, but they don't have the confidence and faith that I have," Hayne added.

"You've got to go all in, I've got no back-up plan. I'm putting all my chips on the table, whatever happens, happens."

Hayne facing massive challenge to crack 49ers' active roster

Asked when he would return to the US, Hayne said he would speak to Tomsula and Baalke shortly.

"I don't think I'll be here too much longer," he said.

"I know it's going to be a huge mountain to climb. I'm excited, nervous, everything you would expect at such a big moment."

"Mentally I'm ready for anything. I'm going to do what it takes.

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"This is a big risk, I'm taking a massive leap of faith."

The 49ers are primarily a rushing (running) team, led by veteran Frank Gore, who rushed for 1,106 yards and four touchdowns in 2014.

They also have a young replacement ready in Carlos Hyde - who ran for 333 yards and four touchdowns last season - as well as mobile quarter-back Colin Kaepernick, who ran for 639 yards and one touchdown in 2014.

San Francisco's punt and kick returner is Bruce Ellington, who returned punts for 188 yards and kick-offs for 614 yards in 2014.

The 49ers had a bad year in 2014, missing the playoffs for the first time in four years. San Francisco had made the NFC championship game three years running from 2011-2013, losing Super Bowl XLVII to the Baltimore Ravens 34-31.

The 49ers are level with the Dallas Cowboys as the second most successful franchise in NFL history, having won five Super Bowls, behind only the Pittsburgh Steelers' six titles.