As the Saudi-backed series has gone on, it has become increasingly more difficult for its players to qualify into the majors.
The most recent evidence of this is with Talor Gooch and the upcoming US Open, and all the drama that's followed.
However, Gooch is one of the 18 LIV Golf players in the field this week in Rochester, New York for the PGA Championship. As is Mickelson.
Also a part of that contingent is Casey, despite the Englishman not initially qualifying for the major.
However, the PGA of America, who runs the tournament, have the discretion to send out special invites to players to meet the field requirements, and it appears as though Casey has made that list.
The current Crushers GC member has historically done very well at the PGA Championship, with a tie for second in 2020 and a tie for fourth in 2021. He was unable to play in 2022 due to an injury, which may have played a role in being brought back for 2023.
PGA of America CEO Seth Waugh told The Times that Casey's special invitation criteria could be put under "good for our event."
The CEO also referred back to Casey's solid major championship history and Ryder Cup involvement when speaking about why the LIV Golf member received a special invitation.
Despite not winning in a major championship, Casey has notched top-10s at each of the four, including his runner-up at the 2020 PGA Championship at TPC Harding Park.
He's also played in five Ryder Cups, representing Team Europe. The biennial event is administrated by both Ryder Cup Europe and the PGA of America.
Casey, 45, joined LIV Golf in 2022 following a series of withdrawals due to his lingering injuries. As a result, his future involvement in the Ryder Cup does not currently seem likely.