Chelsea have denied Crystal Palace's request to allow Conor Gallagher special dispensation to face his parent club in the FA Cup semi-final.
Even though the loan contract forbids them from using the England international against the Blues, changes could have been made to allow it.
The 22-year-old was not involved in the talks and didn't appeal to his parent club to play.
Will he be missed?
Patrick Vieira's side are on a fantastic run of form, winning four of their last five matches.
Indeed, Gallagher has been a huge part of that run and has played in 31 matches, including all four of his side's FA Cup matches thus far.
Furthermore, he has been decisive in the final third, racking up eight goals and five assists in all competitions.
Gareth Southgate has noticed his excellent form on loan and called up Gallagher during the last two international breaks, allowing him to play three times for the England men's national team.
Precedent for this decision
Derby County successfully convinced Chelsea to allow them special dispensation to use loanees Mason Mount and Fikayo Tomori against the Stamford Bridge club in the past.
However, it was a Championship club which was managed by Frank Lampard asking them in a fourth round Carabao Cup match.
The stakes will be much higher for the Blues on Sunday.
Will he return to Chelsea in the summer?
Thomas Tuchel is understood to be a huge admirer of Gallagher and tried to keep him with the squad over the summer.
The west Londoners subsequently allowed the homegrown star to go on loan because the player believed he would get more minutes at Palace.
The Blues are now strongly considering keeping him with the squad next season and giving him a prominent role.
Clubs, including Palace, have inquired about signing him on a permanent deal.
However, the Blues were quoting at least £50 million ($65m) needed to start a conversation over a transfer, pricing many potential suitors out of a move.
His current contract at Stamford Bridge runs until June 2025.