Yet to debut and only 19 years old at the time, the key forward was stunned when the Hawks offered him Franklin's former jumper late last year.
It was a big decision for the Glenelg product, who researched the number's history - which includes 11 premierships between Franklin (two) and Hawks hall of famers Brereton (five), Scott (three) and John Peck (one) – before accepting the honour.
"When they came to me I then went back and had a look at the history of it and made sure it was not going to be too big of an issue with me – that there wasn't going to be too much extra pressure," O'Brien told AFL.com.au.
"I talked to the club and they said 'No, there's not going to be any extra pressure from our end and you shouldn't feel it', so I was happy to take it.
"It's an honour to have it. They haven't placed any further expectation on me, I haven't felt any at all, so it's been good."
With Jarryd Roughead and Jack Gunston in the primes of their careers, Hawthorn can afford not to rush the now 20-year-old.
But many among the brown and gold faithful are eagerly anticipating what might be to come from O'Brien, who was the Hawks' first pick, No.28 overall, in the 2012 NAB AFL Draft.
The mobile 193cm big man whet Hawks fans' appetites in round one last season when, with his first kick in the AFL, he unloaded a 50m bomb and goaled against the Brisbane Lions at Aurora Stadium.
It was a promising start, worthy of elite forwards Franklin and Brereton, who booted 1007 goals in their combined 371 games for the Hawks.
Tim O'Brien was supported by his family on debut in round one, 2014. Picture: AFL Media
Now in his third pre-season, O'Brien is determined to add to his four games and two career goals.
"The club has shown a bit of faith in me and they're happy with how I'm tracking along, so in the future I'm hoping to be playing senior footy every week," he said.
"It will be through my own performances I guess, making the coaches select me and not relying on injury or anything."
O'Brien honed his craft in the VFL last season, booting 13 goals in 11 games, but he admits he needs to bulk up to compete against the AFL's big men.
Tipping the scales at just 83kg last season, he was 17kg lighter than Roughead, who is the same height.
"For me, I would still like to be a mobile player, so I won't be up as big as those guys," O'Brien said.
"I'll stay reasonably lean but put some more size on so I can hold my own against the bigger fellas, more so than I can at the moment."
A big summer in the gym will be matched by a year of learning on the training track, particularly under ex-Melbourne great David Neitz, who is the Hawks' new specialist key position coach.
At his post-season exit meeting, Hawks coach Alastair Clarkson threw down the challenge to O'Brien to learn how to play at either end of the ground.
"That was part of the talk with Clarko, that he would like me to start to learn the game from the back end so then that flexibility is there for me and the team," O'Brien said.
Few play the role better than former Melbourne backman James Frawley, who has impressed with his leadership since he began training with the Hawks' first-to-fourth-year players.
Hawthorn's senior group start the long haul towards a third-straight flag on Monday, but O'Brien said competition is already heating up between the next generation – plus the likes of Frawley and fellow recruit Jonathon O'Rourke – who are desperate to be a part of a premiership team.
And if O'Brien has anything to do with it, it won't be long before Hawks supporters see the No.23 back on the premiership dais.
"It was obviously good for me to be part of the squad that won it, but sitting in the stands you were obviously itching to get out there and you want to play in that game," O'Brien said.
"It does bring drive from the guys that missed out last year and we've seen it already with the younger guys at pre-season training now.
"They all want their chance and when they get it they want to make the most of it.
"There's a fair few on the edge who have played some games who are looking to take that next step, which is healthy for the club."
Now in his third pre-season, O'Brien is determined to add to his four games and two career goals.
"The club has shown a bit of faith in me and they're happy with how I'm tracking along, so in the future I'm hoping to be playing senior footy every week," he said.
"It will be through my own performances I guess, making the coaches select me and not relying on injury or anything."
O'Brien honed his craft in the VFL last season, booting 13 goals in 11 games, but he admits he needs to bulk up to compete against the AFL's big men.
Tipping the scales at just 83kg last season, he was 17kg lighter than Roughead, who is the same height.
"For me, I would still like to be a mobile player, so I won't be up as big as those guys," O'Brien said.
"I'll stay reasonably lean but put some more size on so I can hold my own against the bigger fellas, more so than I can at the moment."
A big summer in the gym will be matched by a year of learning on the training track, particularly under ex-Melbourne great David Neitz, who is the Hawks' new specialist key position coach.
At his post-season exit meeting, Hawks coach Alastair Clarkson threw down the challenge to O'Brien to learn how to play at either end of the ground.
"That was part of the talk with Clarko, that he would like me to start to learn the game from the back end so then that flexibility is there for me and the team," O'Brien said.
Few play the role better than former Melbourne backman James Frawley, who has impressed with his leadership since he began training with the Hawks' first-to-fourth-year players.
Hawthorn's senior group start the long haul towards a third-straight flag on Monday, but O'Brien said competition is already heating up between the next generation – plus the likes of Frawley and fellow recruit Jonathon O'Rourke – who are desperate to be a part of a premiership team.
And if O'Brien has anything to do with it, it won't be long before Hawks supporters see the No.23 back on the premiership dais.
"It was obviously good for me to be part of the squad that won it, but sitting in the stands you were obviously itching to get out there and you want to play in that game," O'Brien said.
"It does bring drive from the guys that missed out last year and we've seen it already with the younger guys at pre-season training now.
"They all want their chance and when they get it they want to make the most of it.
"There's a fair few on the edge who have played some games who are looking to take that next step, which is healthy for the club."
