May announced the end of his 251-game career on Sunday night, saying he did not want to be a distraction for the Demons as they embark on a new era under Steven King.
It followed a period of personal leave for the 34-year-old, who had not been training with the club since a police visit to his house in January.
Cross impressed while training with Melbourne over summer and earnt a rookie list spot before Monday's supplemental selection period deadline.
The 23-year-old was working as a full-time electrician and won Casey's rising star award last season.
He kicked 24 goals in 18 games, including four majors in an elimination final thrashing of Williamstown.
Melbourne's list spot opened up after May called time on his career just days out from the start of the AFL season.
In a club statement, the Demons said May had decided to retire in order to "focus on his family and his own personal growth".
The two-time All-Australian defender and 2021 premiership star was offered up for trade at the end of last season, but could not find a new home.
May and Richmond midfielder Dion Prestia are also fighting charges after a late-2024 brawl in Sorrento on Victoria's Mornington Peninsula.
The former Gold Coast teammates have asked for the charges to be withdrawn, saying they were not present at the brawl.
On Sunday night, May said Melbourne and new coach King "deserve some clean air and no distractions moving forward" and wished them well.
"It's with a heavy heart that I've decided to step away and retire from the AFL," May posted on Instagram.
"It's an incredibly tough decision to make on the eve of the season, but I know it's the right one for myself, my family and the team.
"As a kid from Darwin, all I ever wanted was to play one game of AFL.
"To have lived that dream and had the career I've had is something I'll be forever grateful for."
Like Melbourne, the Western Bulldogs turned to their VFL affiliate to fill their final list spot, adding Footscray forward Will Lewis.
The 194cm forward featured in the Bulldogs' VFL premiership side last year, kicking 40 goals in 19 games for the season, and beat former Carlton player Will White to the rookie list position.
Hawthorn have given former North Melbourne rebounding defender Flynn Perez an AFL lifeline, adding him as a rookie after he helped Sturt win last year's SANFL premiership.
Richmond signed young defender Tom Burton, who won the Western Jets' best-and-fairest award in the Talent League last year.
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