According to L'Equipe (h/t Harry Slavin of MailOnline), the veteran striker struck a deal with the Major League Soccer franchise "three weeks ago."
Sky Sports reported the club are declining to comment on the speculation linking them with a move for the former Sweden international.
Ibrahimovic is out of contract at the end of the season, having previously signed a one-year deal at United. That was after he was released at the end of the 2016-17 term following a serious knee injury.
He will reportedly continue his recovery from injury at United for the time being before making the switch to California. A separate knock picked up against Burnley in December has kept the 36-year-old out of action as of late.
Ibrahimovic posted the following snap of him recovering:
When asked about the striker's future, United manager Jose Mourinho hinted the former Paris Saint-Germain and Barcelona star may be on his way out of Old Trafford.
"Zlatan is in his last year of his contract," Mourinho said, per Slavin. "If that is true and Zlatan wants a future in another country then we are here to help and create conditions for that to happen, not to make his life difficult."
While last season Ibrahimovic assumed a role as United's talisman, at the moment he appears to be a dispensable figure in the quad. These numbers from Sky Sports Statto sum up just how good the striker was for United in 2016-17:
Ibrahimovic turned in many memorable displays, with his two goals in the EFL Cup final win against Southampton particularly impressive.
Injury curtailed his campaign early, though, meaning he was unable to contribute to the final stages of the team's UEFA Europa League run. However, despite his release from contract, he was allowed to recover at United, signed a new deal and worked his way back into the squad.
Since coming back, he's yet to show the same spark, fuelling rumours of a possible exit. Football writer Ives Galarcep believes the move would be a boost for Los Angeles, who are a club previously renowned for bringing in superstar names:
Ibrahimovic has moved clubs frequently throughout his career, and you suspect the challenge of MLS football is one he would be keen to take on. The Galaxy, who have previously snapped up the likes of Steven Gerrard, Ashley Cole, Robbie Keane and David Beckham, feel like an ideal fit for the striker.
The Swede still has the class to thrive in the United States, whereas at United, with Alexis Sanchez recently joining their plethora of attacking options, it's tough to see quite where he fits anymore.