"They became very close... and still went in the ring to try to kill each other," said Wahlberg, who met the late Gatti prior to his portrayal of boxer Ward in the Oscar nominated 2010 movie.
"It's not really a follow-up to The Fighter.... much more of a study of Micky Ward and his relationship that formed from that first fight with Gatti," continued the actor.
> Mark Wahlberg Contraband interview: 'I would do anything to protect my family'
Earlier this year, Wahlberg stated that he hopes Contraband director Baltasar Kormákur will consider directing the sequel to The Fighter.
Contraband opens in UK cinemas on March 16.
Watch Mark Wahlberg in the trailer for The Fighter below: