The former NHLer played two seasons with Crosby in Pittsburgh and said Tuesday the Penguins superstar probably suffered from the long layoff after coming back from a concussion.
"Sidney Crosby needs to be in elite shape to perform at the level that he needs to perform at," Roberts said. "I haven't talked to him, but I don't think he was feeling great. You can't miss that much time in a season, even Sidney Crosby."
Roberts knows about coming back from injury. The former Stanley Cup winner suffered a serious neck injury that forced him to retire at the age of 30.
But he changed his lifestyle, started to train differently and went on to play a total of 21 seasons in NHL before retiring after the 2008-09 campaign.
Crosby played just 22 games in the regular season, registering 37 points (8-29). He added three goals and five assists in the Penguins' six-game loss to the Philadelphia Flyers.
Roberts, 45, says the average person doesn't understand the rigours of what it takes to play professional hockey.
"Look at Mats Sundin," Roberts said of the former captain of the Toronto Maple Leafs. "He took six months off, went back to Vancouver and he told me 'Holy crap, I worked hard off the ice and I can't believe how bad I feel out there."'
Roberts added that any criticism of Crosby for not playing for Canada at the world hockey championship is unjustified.
"If you're not healthy the most important thing when the season is over (is to get ready for next season). Players can't afford to be healing in the summer," he said. "You've got to be getting stronger and preparing for the next year. The summers are not for relaxation to the point that you don't work."
Roberts added in a wide-ranging phone interview that he was captivated by the first round of this year's playoffs, especially the high-scoring Penguins-Flyers series.
"I didn't know what to think in the first round. It was so crazy," said Roberts, who played for Calgary, Carolina, Toronto, Florida, Pittsburgh and Tampa Bay. "I just thought 'Wow, how does that happen to a team like Pittsburgh?' I thought they would win the series, No. 1 and I definitely didn't think we'd be getting eight goals a game."
Roberts also said he regretted comments that appeared a day earlier in the Buffalo News where he called Vancouver Canucks general manager Mike Gillis "a moron."
The Canucks traded Cody Hodgson to the Buffalo Sabres prior to the trade deadline. Gillis criticized Hodgson, who trains with Roberts at his gym in the summer, at his end-of-season news conference.
"I spent more time on Cody's issues than every other player combined on our team the last three years," the Canucks' GM said last week.
The comments made it clear that Hodgson, who suffered a serious back injury while with the Canucks, had requested a trade out of Vancouver.
"I obviously didn't choose the right words. I don't have anything personally against Mike Gillis or the Vancouver Canucks," Roberts said Tuesday. "It was a little unjustified for me to go that far and I apologize for that word I used.
"But in Cody's defence, I've been with this player for three years, I see his commitment, dedication, the type of person he is, the way he treats people. I see how hard he's worked through a very tough time early in his career and I just felt very strongly that I had to take a stand for this young man."