Carlo went down after Wilson went hands-high to his head in the corner behind the Boston net, smashing the defenseman's head into the glass with 90 seconds left in the first period. Carlo absorbed a cross-check from Jakub Vrana on his way to the ice and remained there for several minutes.
Cassidy said Carlo left the arena in an ambulance and went to a hospital but could not confirm that he suffered a concussion.
"Clearly looked to me like he got him right in the head. A defenseless player, a predatory hit from a player that's done that before," Cassidy said of Wilson. "I don't understand why there wasn't a penalty called on the ice. They huddled up, but I did not get an explanation why."
During his eight-year career with the Capitals, Wilson has been one of the most penalized -- and most suspended -- players in the NHL. He is 10th among active players for penalty minutes, trailing only those who have been in the league five or more years longer than him.
He was not made available for comment after the game.
The music went silent in the empty arena after Carlo was hurt, and the Bruins' bench could be heard cussing out Wilson. When Carlo finally got to his skates, the only noise was his teammates banging their sticks against the boards.
No penalty was called.
When the teams came out for the second period, Bruins center Patrice Bergeron skated over to Wilson and spoke to him as he stretched out. Capitals star Alex Ovechkin skated by to monitor the situation, as did an official.
Players began shoving each other after the next whistle, and Capitals defenseman Brenden Dillon was sent off for roughing in a transparent makeup call. With about six minutes gone in the period, Boston's Jarred Tinordi and Wilson dropped their gloves.
"Sometimes when that stuff happens and there's no call, the players kind of settle it on the ice in their own way, and we felt that we pushed back and did what we could do and won the hockey game, and tried to let that particular player know that that was unnecessary," Cassidy said.
He added: "I assume it will get looked at by the National Hockey League."
The Bruins responded to Wilson's hit with a three-goal second period and tacked on another in the third to win 5-1.
"Put the fight aside, the guys came out with four goals [in a row] there,'' said Tinordi, who was playing just his second game with the Bruins since they claimed him off waivers from Nashville.
"How close this group is, I'm not surprised to see the boys respond in a big way after one of our guys goes down. You can't have guys taking liberties with our players out there.''
The Associated Press contributed to this report.