The 25-year-old joined the Mavericks earlier this year on a lucrative three-year deal from the Houston Rockets, but has struggled with fatigue issues during his side's pre-season games.
Carlisle believes that the problems stem from the player's weight, which was increased by 20 pounds in the off-season from 215lbs to 235lbs, and is adamant that Parsons needs to lose at least 10 pounds.
"He looked tired out there tonight to me, and his shot is short," Carlisle told reporters. "He's working on losing some weight. He's a little bit heavier than he's been.
"He's up over 230, and we want to see him get down to at least 225. That's a work in progress, and tonight's one of those nights where I think the extra weight was a hindrance."
The Mavericks open their 2014-15 season against the reigning NBA Champions, San Antonio Spurs, on October 28.