After the hit on Sandin, Maple Leafs center Jason Spezza drove his left knee into the face of Pionk, who was stickless and on his knees trying to clear a puck. Spezza has been offered an in-person hearing with NHL, and likely will be suspended.
In-person hearings are required for any suspension that could be at least six games. The date and time of Spezza's hearing have not been announced.
Sandin skated off the ice after the knee-on-knee hit on his right knee.
The Jets won Sunday's game 6-3.
After a so-so November, Winnipeg has rallied with two victories in a row to improve to 12-8-4. The Jets are in second place in the Central Division, seven points behind the Minnesota Wild.
Pionk is a valued piece on their back line. Through 24 games this season, he is averaging 22:08 time on ice, and has chipped in with two goals and 16 points.
The Associated Press contributed to this report.