He didn't have enough strength or size. He didn't have the defensive responsibility or the knowledge.
Four years later, the Boston Bruins forward has all of that. He has turned himself into one of the best scorers in the NHL, with eight goals in seven games this season, second to Toronto Maple Leafs forward Auston Matthews, who has 10 in eight games.
His goal in a 3-2 loss to the Edmonton Oilers on Thursday gave him 102 for his NHL career. A hat trick against the Detroit Red Wings on Saturday gave him 101; he got to 100 in 259 games, making him the third-fastest Bruins player to reach the milestone (Barry Pederson, 187; Dit Clapper, 247) among those who began their career with Boston, and the third-fastest Czech Republic-born player (Petr Klima, 231; Jaromir Jagr, 245).
Video: BOS@EDM: Pastrnak wrists one by Talbot to tie it
"I think it's a lot harder now to get to the places to score 100 goals," Klima told NHL.com by phone Monday. "It was a lot easier to score goals when I played in the '80s and '90s and Jagr in the '90s.
"I think he's going to be the next Jagr if he continues [like this]. There's obviously only one Jagr, but [Pastrnak is] playing well, he's very young, and he's got all his career in front of him."
Klima finished his 13-season NHL career with 313 goals, leaving after 1998-99. Jagr most recently played in the NHL last season with the Calgary Flames and scored 766 goals in 24 seasons; he is third behind Wayne Gretzky (894) and Gordie Howe (801).
"I wouldn't compare him to Jagr. Jagr was Jagr," said Bruins teammate and fellow Czech forward David Krejci, who played with Jagr in Boston during 2012-13. "But I think [Pastrnak], he's going to be known as David Pastrnak, one of the greats, especially from [the] Czech [Republic]. If you go down in the history book, you're going to see Jagr in the '90s, early 2000s, and then you're going to have Pastrnak.
"I wouldn't compare them, but I would put them in their own category and no one's getting close to them."
But Krejci, for one, didn't necessarily expect this.
Though they have been teammates for five seasons and have played together for the Czech Republic, Krejci said he didn't see this level of play, of goal-scoring, of stardom, coming for his countryman.
"To be honest, maybe not," Krejci said. "I knew he has lots of skill, but if you go [back] and look for his first or second year in the League, it's such a big jump. He always had the skills, but he works really hard in the summer and his shot has just improved so much. Now he has confidence and if you put all those tools together -- his confidence, his shot, his skills -- then it's hard to stop."
Pastrnak has a lot of work to do to approach Jagr's numbers. But the right wing, who has earned a spot on the Bruins' top line with Brad Marchand and Patrice Bergeron, has never shied away from hard work.
"A lot of work has been done, obviously it was four years, so a lot of work," Pastrnak said. "Experience has a lot to do with it as well, and confidence. Every year [I] try to get better.
Video: DET@BOS: Pastrnak cashes in on two-on-one for hatty
"I just played hockey and tried to get better. I know I'm a skill guy, since I was a little kid, always loved to score goals and being this kind of offensive forward. So I've just been working on it more obviously since I joined the NHL, but been working on this game for all my life."
That is what has gotten him to this point.
Though Pastrnak's hat trick Saturday was impressive, his previous game, against Connor McDavid and the Oilers on Oct. 11, might have been more notable. McDavid scored his first goal of the season early in the first period, taking the puck from the red line in, accelerating past defensemen Zdeno Chara and Charlie McAvoy.
But Pastrnak was not to be outdone. Later in the period, the 22-year-old went forehand-to-backhand with a deke around defenseman Matt Benning that could end up as one of the best goals scored all season.
"Every year he comes into training camp with more moves," Krejci said. "I didn't think there's any more moves. But he can do them just like McDavid, with full speed. He has great speed, too. When your hands are catching up with your speed, then that's a weapon, and he's got all the tools."
Pastrnak (6 feet, 194 pounds) has added to his arsenal over the past four seasons, building on the abilities that led the Bruins to select him in the first round (No. 25) of the 2014 NHL Draft and likely making more than a few teams regret passing over him. He had NHL career highs in goals (35), assists (45) and points (80) last season.
"He was always dynamic," said Bruins coach Bruce Cassidy, who coached Pastrnak for 25 games in 2014-15 with Providence of the American Hockey League. "Always had the good 1-on-1 ability to create on his own, even in Providence at 18 he was good at that. Where I think the biggest difference [is] from now to then was his shot. I didn't see it coming along this well, to be honest with you.
"He scored a lot of goals in tight, deking, and some wrist shots, but that one-timer, he's really built that into his game as one of the elite shooters now."
It isn't just the shot, though. It's that Pastrnak has become more responsible on the ice, a generally inevitable consequence of being on a line with Bergeron and Marchand. It happened to Marchand when he was put on a line with Bergeron.
Video: EDM@BOS: Pastrnak dangles, scores pretty PPG
"His confidence level is through the roof right now," Marchand said. "But I think you're starting to see other areas of his game become a lot better. He's winning a ton of puck battles. He's way stronger now. It's so hard to take the puck from him. And then you add that with his playmaking ability and scoring capability and the way he's taking care of pucks in our zone, [he's] continually getting better."
They could see it coming. And they still couldn't have predicted this.
"You could see the skills from Day One," Bergeron said. "He's a very smart player with the puck and when you add hard work and wanting to be better, you have a perfect recipe.
"I think the sky's the limit for him."
Or perhaps Jagr's the limit.
Though Klima cautioned that there is only one Jagr, Pastrnak is clearly becoming one of the NHL's best scorers.
"That's the hardest job in hockey, to score goals," Klima said. "And he's good at it."
Before he hung up, Klima had one more thing to add.
"Just tell him I wish him luck," he said. "I hope he beats all the records."