Geelong has lost young ruckman Shane Mumford to Sydney, but the Cats have been successful in securing the services of Fremantle defender Marcus Drum.

The Cats accepted Sydney's offer of a second round draft pick (No.28 overall) for their rookie ruckman, while the club offloaded its third round pick (No.49) for Drum.

Geelong agreed to allow Mumford, a 23-year-old who has played just 21 games and is still on the club's rookie list, to move to the Swans on Thursday after the club conceded it would not be able to match the Swans' massive offer to a player that was left out of the Cats' grand final team in favour of Mark Blake this year but showed great improvement in 2009.

The Swans have offered Mumford a four-year deal believed to be worth $1 million - an incredible offer for a youngster that was only on a rookie contract and base match payments at Geelong.

Sydney has identified Mumford as its replacement for No.1 ruckman Darren Jolly, who was officially traded to the Magpies on Wednesday in return for the Pies' first round and third round draft picks (selections 14 and 46 overall) after he expressed his desire to return to Victoria for personal reasons.

The Cats attempted to convince the young man, who they plucked from obscurity from Bunyip in country Victoria, to stay with the club but knew they had no hope of matching the Swans' massive offer.

"The reality is that we could not and would not compete with the dollars that Shane has been offered," Geelong's general manager of football operations Neil Balme said on the club's website.

"It's well known that we want to keep our group together and all of the players have accepted that to do that they have to forego bigger offers from other clubs to achieve that goal. Shane has chosen not do that that, and while we are disappointed to see him go, we will not deviate from our philosophy."

Drum has played just 22 matches for the Dockers since being taken at pick 10 in the 2005 draft.

The 22-year-old is the nephew of former Geelong rover and Fremantle coach Damian Drum.

"We see Marcus as a versatile player that can fit into our structure. He has played some good games at Fremantle and we feel that his best football is still ahead of him," Balme said.

"Marcus is only 22, and is a quality person. He was a top 10 draft pick just four years ago, and has talent and a good work ethic, and sees the opportunity to play as the most important thing given our tight salary structure."