However, Meehan's management has been in dialogue for several weeks with Manly officials about the young star's intent and focus on rugby league, which was split with his desire to continue boxing.
Despite investing the entire off-season into the talented prop, Manly advised Meehan they would support whichever decision he made.
"It was decided it was in the best interest of all concerned that Willis made a commitment to one sport," Sea Eagles football operations manager Gareth Holmes said.
"With the time needed in an NRL full-time squad, Willis chose to go in a different direction and we wish him well in his endeavours."
Meehan wasn't the only loss for the Sea Eagles on Tuesday. Coach Trent Barrett will have to call upon his depth in the backline in the pre-season fixtures after winger Matt Wright broke his hand at training.
Wright was due to play in the Auckland Nines next weekend but was ruled out after breaking a bone in his left hand during a contact session at Narrabeen.
Barrett said Wright had been one of the club's best performers during the pre-season.
"Unfortunately, there are plenty of collisions in training these days and Matthew was a victim of this," Barrett said.
"The good news is that he will be fit for the start of the premiership against Parramatta at Brookvale Oval (on March 5)."
Barrett will name a replacement for his Auckland Nines squad in the coming days.