Gilbert Enoka has been hired by Chelsea manager Graham Potter.
Enoka was the mental skills coach behind the "no d***heads" policy at the New Zealand national rugby team.
He has been working with the All Blacks for the past 22 years, with the last seven as the manager for leadership.
The 15 years before he took on that role, he worked as the team's mental skills coach.
Enoka will be taking up a "short-term consultancy role" with Chelsea.
It will be his first job in football, but he is widely considered to have been an important part of the All Blacks' success over the last 20 years.