Leafs' Armstrong could miss four weeks
Armstrong was hurt in the first period of a 3-1 win over the Florida Panthers on Tuesday night.
The Leafs also announced Wednesday that they have recalled forward Luca Caputi from the Toronto Marlies of the American Hockey League.
Armstrong has one goal and 11 penalty minutes in eight games this season. He signed a $9 million, three-year deal over the summer.
Caputi had one goal and one assist in six games with the Marlies.