Donnie Yen's wife publicly expressed her worries that Yen might get hurt by Mike Tyson. However, it was Yen who ended up fracturing Tyson's index finger while filming one of the fight scenes.
Donnie Yen studied Mike Tyson's past matches to prepare physically and mentally for the fight scenes with him. As a former world heavy weight champion boxer, Tyson punches over 1,500 foot pounds of force in the ring.
The real Bruce Lee began learning Wing Chun from Ip Man when he was sixteen years old, and he passed away when he was thirty-two years of age. Danny Kwok-Kwan Chan, who played Lee seeking Ip to be his master in the movie, was forty at the time of filming.
The Muay Thai fighter is Simon Kook. He is also known to be Tony Jaa's stunt double in the movie Skin Trade (2014).
The producers originally planned to convey Bruce Lee's likeness and portrayal digitally through the use of CGI superimpose on a body double with facial motion capture performance, but it was later dropped after the Bruce Lee's estate threatened legal action over copyright infringement for allegedly not acquiring permission to use any intellectual property rights associated with Bruce Lee.