Former Western Bulldogs and Richmond coach Terry Wallace, believes Cats premiership defender Tom Lonergan may no longer be in Geelong's best 22.

Lonergan, 33, is most likely in his final season at the Cattery. However, Wallace has suggested that he may even struggle to play out the season, with the game seemingly passing him by of late.

“Is Tom Lonergan in the Cats’ best side?” Wallace said on SEN’s The Run Home on Tuesday night.

“We all love Tommy, and we love everything that he’s done for the footy club, so there is always the utmost respect for Tom Lonergan.

“But the side without him last Thursday night looked more mobile with the likes of Zac Tuohy, Cam Guthrie, Andrew Mackie and Tom Stewart."

Lonergan was rested from Geelong's side last week, with the Cats recording a thrilling three-point win over Port Adelaide at Simonds Stadium, leaving Wallace to question his effectiveness in the side.

Lonergan has long been one of the best key big defenders in the league, shutting down key forwards week in, week out, however, the game has evolved from the long kick to a one-out key forward inside 50.

“There was more run. It looked more free-flowing with him out of the team," Wallace said.

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“Do the Cats need him there just because he is going to be the one that stops, and restricts, the big boys?

"Or can the likes of Henderson and Koldjashnij do the job adequately enough that its gives the Cats more of a springboard?

“Because the game has become more and more about springboard from defence and Tommy doesn’t provide that.”

Lonergan, who stands at 197cm tall, has played 195 career games with the Cats, winning the 2011 premiership and he finished ninth in Geelong's best and fairest last season.

With Harry Harry Taylor moving to the forward line, Lonergan is the Cats go to key defender down back. Lachie Henderson (196cm) has been impressive since moving from Carlton and can also perform a shut down role on a key forward.

However, Geelong's next key defender at the moment, is either Jake Kolodkashnij (193cm) or Andrew Mackie (192cm), who would both been undersized against the best key forwards in the game.

As long as the Cats keep Taylor up forward, Lonergan and Henderson will most likely both be needed down back.