Essendon will be looking to secure "compelling compensation" from Carlton after dashing defender Adam Saad nominated the Blues as his club of choice.
Saad, who has played 61 games for the Bombers after 48 at Gold Coast, informed Essendon on Tuesday of his wish to move on.
The 26-year-old averaged a career-high 18.9 disposals per game this season, despite the shortened game length, and his departure is another big blow to Essendon's hopes of turning around a poor 2020.
The Bombers have already lost fellow rebounding defender Conor McKenna to retirement, while free agent Joe Daniher and forward Orazio Fantasia could also be on the move.
Daniher has been heavily linked to the Brisbane Lions, while Fantasia could return home to South Australia despite being contracted for 2021.
Saad is set to earn a five-year deal at Carlton, assuming a trade with Essendon can be done.
The Bombers are likely to request Carlton's first-round draft pick.
"We put forward a significant offer to Adam and we are disappointed in his decision to pursue a playing future elsewhere," Essendon's recruiting manager Adrian Dodoro said
"Although we wish Adam all the best, he is not a free agent and therefore a suitable trade will need to be forthcoming from Carlton. Clearly, there is an expectation of compelling compensation for a player of Adam's calibre."
Saad's decision is another big boost for the Blues, who have also attracted GWS free agent Zac Williams.
Meanwhile, Jackson Hately is the latest player to want out of the Giants, with the midfielder requesting a trade to Adelaide.
Taken at pick 14 in the 2018 draft, Hately is determined to return to his home state and has picked the Crows as his desired club.
"Jackson has informed the club of his hope to return to South Australia so we will now investigate trade options with a view to getting the best possible outcome for the Giants," GWS football manager Jason McCartney said.
The 19-year-old from Central Districts played 13 games for GWS after debuting in round five last year.
He joins defenders Williams and Aidan Corr in requesting moves away from the Giants, who failed to make the finals this year after being badly beaten by Richmond in the 2019 grand final.
Veteran defender Heath Shaw has not been offered a new contract, while ruckman Sam Jacobs has retired.
Star forward Jeremy Cameron is out of contract and yet to re-sign, while Hately's fellow 2018 draftee Jye Caldwell has been assessing his options after interest from rival clubs.
Melbourne vice-captain Jack Viney has signed a new five-year deal with the Demons, tying him to the club until the end of 2025.