The 26-year-old marking forward shocked teammates with the news he would attempt to make it as a punter in America, telling them the opportunity only became real a fortnight ago.

With his contract due to expire at the end of 2018, he said the offer was too good a chance to pass up.

"This was a difficult decision to make, but ultimately the opportunity was too good to refuse," Griffiths said.

"It certainly wasn't something I had been contemplating and only arose two weeks ago.

"It was tough telling my teammates and coaches this morning but they understand and support my decision."

Griffiths suffered his first concussion for the season in round two in 2017 and then missed 11 weeks after suffering a second head knock three weeks later in the VFL.

A shoulder injury later in the year ruled him out of AFL calculations but he returned to play with Richmond in the VFL finals and watched from the sidelines as the Tigers stormed to their first premiership in 37 years.

The early season loss of Griffiths as a key forward saw the Tigers adopt an unusual forward combination with bunch of pacy small forwards surrounding key forward Jack Riewoldt.

The set-up played a key role in the Tigers' ability to put opponents under enormous pressure.

Griffiths played 63 games with the Tigers wearing a helmet from 2016 onwards after being concussed in the pre-season when he collided with Fremantle's Aaron Sandilands.

A booming kick, he was pick 19 in the 2009 national draft. While he is a loss, the Tigers' draft pick Callum Coleman-Jones should be able to cover his departure.

Meanwhile reigning Adelaide best and fairest winner Matt Crouch has extended his contract with the Crows until the end of 2021.

The 22-year-old was one of the AFL's most improved players, earning All Australian selection and he was one of the Crows' few good performers on Grand Final day.