The five-time Champions League winner recently departed Premier League giants Manchester United after a four-year stint that included more than 100 appearances.
However, the deal is now under investigation by the league's governing body after the MLS uncovered potential tampering in Inter Miami's acquisition of the rights to sign Casemiro.
Under the MLS' rules regarding signings of overseas players known as the 'discovery process', each club can confidentially submit a list with as many as seven foreign players for whom they hold priority to recruit should they agree to terms with the player.
The discovery process does not give clubs exclusive rights to sign overseas players, but clubs can sell or swap discovery rights with one another, as was the case with German player Marcos Reus in 2024 when LA Galaxy agreed to give Charlotte FC $400,000 of General Allocation Money over two seasons in exchange for the rights to recruit Reus.
The MLS did not disclose details of the tampering allegation made, nor specify what part of the discovery rights process may have been compromised, such as whether Inter Miami entered into direct negotiations with Casemiro before acquiring discovery rights from LA Galaxy.
“Major League Soccer is reviewing a tampering allegation against Inter Miami CF,” the MLS statement said.
“The league is gathering all relevant information and will refrain from further comment until the review is complete.
"While Inter Miami CF and the LA Galaxy have reached a settlement for the Discovery Priority to sign Casemiro, the terms will be released upon conclusion of the tampering investigation.”
Inter Miami won their most recent match over Chicago Fire 3-2, spoiling Robert Lewandowski's MLS debut, with the contest somewhat overshadowed by a farcical own goal involving Miami goalkeeper Rocco Rios and centre back Ian Fray.
A simple backpass from Jamaican defender Fray rolled gently into the side of the net after Rios completely missed an attempted clearance with his right boot, inadvertently opening the scoring for Chicago Fire.