In an email to The Canadian Press, Leiweke said the report was "not true" and that he's "focused on the season at hand."
The denial came after Elliotte Friedman of Hockey Night in Canada sent out two tweets on his verified Twitter feed Tuesday.
"Hearing MLSE president/CEO Tim Leiweke will be leaving the company soon," Friedman tweeted. "Not sure of where he's going, but hearing the reason is he is looking for a new challenge."
Leiweke was named president and chief executive officer of MLSE in April 2013 and not long after made headlines by conceding he already had the Toronto Maple Leafs' parade route planned out for the team's next Stanley Cup.
MLSE counts the NHL's Leafs, NBA's Raptors, AHL's Marlies and Toronto FC of Major League Soccer among its properties.
Leiweke previously worked as president and CEO of AEG, which owns the NHL's Los Angeles Kings, NBA's Lakers and the Galaxy of MLS.