Kessel said the media's coverage of Phaneuf was "embarrassing" and that they should be "ashamed."
"I think the way the media treats Dion in this city is embarrassing," Kessel said, according to ESPN.
The Leafs are 25-33-5 this season. Their 55 points are tied for second-worst in the Eastern Conference and fourth-worst in the NHL.
Phaneuf was considered a trade possibility before Monday's trade deadline, but the Leafs held on to the 29-year-old defenseman. Kessel blasted Phaneuf's critics on Tuesday.
"Is it his fault we're losing? No," he said, according to ESPN. "Did he build this team? No."
Toronto plays at the Florida Panthers on Tuesday night.
- Stanley Kay