Rey Mysterio is technically working for WWE as a free agent at the moment.
This is according to Dave Meltzer of the Wrestling Observer/Figure Four Online, who reports that the pro-wrestling legend is yet to sign a new deal with the promotion following the expiry of his last contract, which was signed back in September 2018.
Recent months have brought several reports on Mysterio's wrestling future, with most suggesting that his contract renewal has been held up as WWE's policy is to not offer bumper new deals in the middle of the global health crisis. This is undermined somewhat by Drew Gulak, who recently let his WWE deal expire before negotiating a new one and returning, all within a week.
Mysterio has remained a steady presence on Raw despite his non-contracted status. Him and son Dominik are currently embroiled in a long-running storyline with Seth Rollins, with the upcoming Extreme Rules pay-per-view (19 July) a likely blow-off point for their feud.
Dominik is currently training under his father ahead of transitioning into a full-time wrestling career, having gotten physical with Rollins and his crew several times over the past few weeks.