Brady Tkachuk should be returning to the Sens lineup this week. He could give Pettersson a run for his money.
I don't see how since he's so far behind in points, goals etc. Unless Pettersson misses a whole bunch of games. Which leads me to the next point: The Calder is definitely Pettersson's to lose at this point. The youngster has been absolutely insane and judging by eye test, it's not a fluke. Unless he goes down on a serious injury, I absolutely expect him to finish the season as a PPG player and snatching the Calder with no one even close.
On top of that, I can see a case for both Heiskanen and Dahlin being bigger threats to Pettersson than Tkachuk, though I fully expect both of 'em not to finish anywhere close to him for it be a real competition.
edit:
Nevermind, the quoted post is from early November. My bad.