The Lions got the better of Thomas Christiansen's Leeds 1-0 at home in the Championship at the weekend.
Aiden O’Brien’s goal in the 73rd minute proved to be the difference between the two sides at The Den on Saturday afternoon.
Morison was on the books of Leeds from 2013 and 2015, but the 34-year-old striker failed to make a massive impact at Elland Road.
The Welshman has fared much better at Millwall and has established himself as an important player for the Lions.
“I couldn’t care less about that,” Morison has been quoted as saying by News at Den about the win being special. “I ain’t bothered about that, that’s what you lot [press] want to talk about.”
Over the course of the 90 minutes at The Den on Saturday afternoon, hosts Millwall had 46% of the possession, took 20 shots of which six were on target, and earned 14 corners, according to BBC Sport.
Visitors Leeds had 54% of the possession, took one shot which was not on target, and earned two corners, according to BBC Sport.