Monahan scored 22 goals as a rookie last season and was fifth on the Flames with 34 points in 75 games.
It's easy to forget Monahan doesn't turn 20 until next month. At six-foot-two and 185 pounds, he cruises into the faceoff circle with a confident demeanour. He says he's about eight pounds heavier than his rookie weight.
"I focused on the stuff that I really needed to focus on, so I did a lot of strength training and explosive stuff and really focused on diet," Monahan said Monday in Calgary.
When Monahan turned up wearing a tight T-shirt at a summer hockey camp run by Bob Hartley, the Flames head coach did a double take.
"He just said I look like a man," Monahan said. "I worked hard this summer so I think it's paid off. It obviously doesn't matter to me if other people notice it. It all comes down to me.
"Whatever work I put in, I feel it on the ice and I think that's the biggest thing."
Drafted sixth overall by the Flames in 2013, the centre from Brampton, Ont., had a legitimate shot at making a rebuilding Flames roster as an 18-year-old last fall.
But his offensive contributions outstripped expectations. Monahan was the first Flames rookie since Jarome Iginla in 1996-97 to score 21 goals.
Monahan did finish the season minus-20, but few Flames were in the black in plus-minus on a team that finished 27th in a 30-team league.
Monahan put up impressive numbers despite a hairline fracture in his foot that kept him out seven straight games in November and December.
With top-line centre Mikael Backlund sidelined with injury, Monahan averaged well over 18 minutes per game in the last five games of the regular season.
He was then invited to play for Canada at the world championships, where he had two assists in seven games, to pack even more experience into his rookie campaign.
"Suddenly he's more talkative. It's just part of feeling more confident," Hartley said. "Now he knows that he really has a spot on this team. He knows about the NHL.
"We have big expectations about Monny, but what makes me feel the most comfortable is Monny by himself sets some real high expectations."
There's inevitable questions about avoiding "the sophomore slump." Monahan will no longer surprise opposing teams, so he'll need that additional strength.
"Here's my explanation on sophomore slump," Hartley began. "Number one, as a rookie, the other teams don't know you very well so sometimes you get the fifth or sixth defenceman, you get the third line playing against you. Sean Monahan will get much more attention from opponents this year.
"Number two, and that's where I feel so good, is many young players get a great first year and they sit (on it). Looking at Sean's fitness test, just looking at him, you can tell that he spent the summer working out. He's on a mission. That second part doesn't worry me one bit."
New Flames winger Mason Raymond spent time on Monahan's wing in a split-squad exhibition game Sunday against the Edmonton Oilers.
"Yeah, young kid. Here I am nine years older," Raymond said. "He's very mature for his age. I've skated with him for the last month, but it's impressive to see how he handles himself and understands what's expected of himself.
"It's a treat to play with him so far. We're learning each other and starting to gel a bit."
After a few skates and the exhibition game, Hartley has noticed there's more authority in Monahan's game.
"Battles in the corners, probably faceoffs also," the coach said. "I felt like last night he won many big faceoffs with us. Going around the defencemen, battling for loose pucks, that's where the opponents will notice it.
"He'll be able to go with the big boys and play in those tough areas. It's impressive."
The Flames have several centres in camp and the depth chart is fluid up the middle. Monahan, Backlund, Matt Stajan, Joe Colborne as well as prospects Max Reinhart, Markus Granlund, Bill Arnold and Corban Knight are battling for ice time and jobs.
There's room for Monahan to up his stock at main camp in the absence of 25-year-old Backlund, who has yet to participate in a full practice because of an abdominal injury.
"I don't have any news to tell you, but I'm worried," Hartley said ominously. "He's still not on the ice. I'd like to see him on the ice, that's for sure."
Forward Sam Bennett, the highest draft pick in Calgary Flames history at No. 4 this year, is expected to practise Tuesday after sitting out the first few days of main camp with a groin injury.
Calgary got down to 58 players Monday when the following players were assigned to their respective major junior teams: defenceman Jason Fram (Spokane Chiefs); winger Brandon Magee (Victoria Royals); goaltender Mason McDonald (Charlottetown Islanders); winger Hunter Smith (Oshawa Generals).
The Flames have three pre-season games in as many days starting Wednesday when they take on the Arizona Coyotes in Sylvan Lake, Alta. Calgary then plays a home-and-away against the Vancouver Canucks on Thursday and Friday.
Monahan's mom Cathy relocated to Calgary last season to oversee her son's first year in the NHL. Monahan has taken a step forward in off-ice independence by moving in with Flames forward Lance Bouma to start this season.
Who is going to cook?
"Lance," Monahan said firmly.
Note to readers: This is a corrected story. An earlier version had the wrong first name for Max Reinhart.Suggest a correction