David Luiz has told Chelsea he wants to leave to join Arsenal before the transfer window shuts on Thursday, according to Sky Sports.
Luiz trained separately from his team-mates on Wednesday after making his feelings known.
He is thought to be one of a number of central defenders on Arsenal's shortlist, but the Gunners are still to make a formal offer.
Chelsea, for their part, want to keep Luiz because they are unable to sign an immediate replacement under their current transfer ban.
Luiz had seemed to commit his future to the Blues when he signed a contract extension in May, but his stance has now changed.
Background to the deal
Luiz is in his second spell at Chelsea after returning from PSG ahead of the 2016/17 season.
He has made over 100 appearances over the course of the past three seasons, winning the Premier League, FA Cup and, most recently, Europa League after Chelsea beat Arsenal 4-1 in the final.
There is of course an intense rivalry at play, with the two London sides set to compete for a top-four spot this year, but still it is not uncommon for them to exchange players.
Olivier Giroud (January 2018) and Petr Cech (June 2015) are the pair who have most recently changed allegiance.
A frantic end to CB search?
Arsenal have broken their transfer record this summer to sign Nicolas Pepe from Lille, but have yet to recruit a potential remedy for their defensive frailties.
They shipped 51 league goals last season, more than anybody else in the top six.
With time running out until the transfer window closes on Thursday evening, they are still trying to strike a deal for a centre-half.
"If we can on the last day, we will try to sign another centre-back, but one who has the capacity to help us," Emery confirmed to Sky Sports News.
"I'm happy with our defensive players. We are working in the last minute, we are also taking the possibility that we can add some players who can help us with good performance."
Alongside Luiz, RB Leipzig's Dayot Upamecano is reportedly on their shortlist.
There could also be a last-ditch attempt to overcome the present impasse in a proposed deal for Celtic left-back Kieran Tierney.