CARLTON has plenty of options to replace Sam Docherty this season, but no one player can fill the gaping hole left by the injured defender's absence, Blues coach Brendon Bolton says.

Docherty's 2018 season ended before it began when he ruptured his left anterior cruciate ligament at training last November. 

Bolton told AFL.com.au most people at Carlton had been "really emotional" upon learning of Docherty's injury, with the coach freely admitting: "There was nearly a tear in my eye as well." 

It was an understandable response given Docherty, 24, was coming off two outstanding seasons – he won Carlton's best and fairest award in 2016 and secured his maiden All Australian selection last year – and had grown so much as a leader that he would subsequently be appointed the club's joint vice-captain, alongside Patrick Cripps. 

But the Blues quickly moved on and Bolton was pleased with the "healthy competition" that developed over the pre-season to step into Docherty's position.

The Carlton coach said recycled recruits Aaron Mullett (North Melbourne) and Cam O'Shea (Port Adelaide) were among the players who had pressed their cases, along with Irishman Ciaran Byrne, who made an encouraging return from a knee construction late last season, and second-year speedster Tom Williamson.  

Bolton stressed, however, that it would take a collective effort from the Blues' back six to cover Docherty's absence.

"I don't think one player will fill [the hole left by Docherty]. You can't replace an All Australian that easily," Bolton said. 

"Multiple players will need to step up to fill a percentage of Sam Docherty's role, particularly with regards to his leadership. 

"All of the players are committed to doing that, which is great."

The other sizeable on-field vacuum the Blues will have to fill this year is that left by Bryce Gibbs' departure to Adelaide.

Along with Marc Murphy and Cripps, Gibbs had shouldered a disproportionately heavy load in Carlton's midfield over recent seasons.

Bolton acknowledges Gibbs' exit could cause the Blues some short-term pain, but is confident the club's midfield future is bright. 

"I don't think you can replace a 200-plus-gamer in Bryce Gibbs overnight but it gives opportunity for Sam Petrevski-Seton, Matthew Kennedy, Darcy Lang, Paddy Dow, Zac Fisher and Lochie O'Brien to grow in and around Paddy Cripps," Bolton says. 

"We lose some experience but we gain more players – young in age but with a lot of talent – and they get an opportunity to grow this club and take it forward."

Bolton said the Blues' first two picks in last year's NAB AFL Draft, Dow (No.3 overall) and O'Brien (No.10), were both "in the mix" to debut in the round one blockbuster against Richmond.

"Paddy had an interrupted start with his shoulder but since then what we've liked is how he comes out of a stoppage. He moves really quickly and gets out the front of stoppages," Bolton said. 

"Lochie O'Brien is a running machine, an outside mid with a long left foot. He competes with the Curnows (in running drills), which says what sort of engine he's got. 

"They're now just learning how to play in a team structure, but their natural talents are exciting and let's see where that gets to."