The AAF team with the lowest win-loss percentage held the first crack at Manziel through the league's waiver process.
AAF chairman Tom Dundon said earlier this month that Manziel would not receive any special treatment in the league, and will get the same three-year, $250,000 deal that every player gets.
Manziel most recently played in the Canadian Football League with the Montreal Alouettes, but he was released by the team in February after violating the conditions he agreed to in order to play in the league. He's their second quarterback this season, after the team started with Christian Hackenberg but later benched the former Penn State quarterback.
According to Shefter, Manziel would have been allocated to San Antonio, but the Commanders waived his rights, so the controversial quarterback will go through the league's waiver system.
The Memphis Express have the AAF's worst record at 1-5, followed by the Salt Lake City Stallions at 2-4, with the Arizona Hotshots and Atlanta legends both sitting at 2-3.
Manziel signed the AAF standard player agreement on Saturday, according to ESPN's Adam Schefter, which will officially allow teams to sign the quarterback.
Information from The Associated Press was used in this report.
The 26-year-old Manziel passed for 1,290 yards and five touchdowns in eight games last season with the CFL's Montreal Alouettes, which acquired him in a mid-season trade with the Hamilton Tiger-Cats.
Manziel was a first-round draft pick by Cleveland, but quickly fizzled out there.
Manziel eventually ended up signing with Hamilton in May 2018 but was unable to get on to the field behind starter Jeremiah Masoli.