Clarkson, 30, is in his ninth NHL season. In 58 games this season, he has scored 10 goals and totaled 15 points with a -11 plus/minus mark. The Blue Jackets will be the third team of his career. He spent his first seven years with the New Jersey Devils.
Horton, 29, has not played this season due to a degenerative back injury. He played 36 games last season, scoring five goals and adding 14 assists. In July 2013, he signed a seven-year contract worth $37.1 million with Columbus.
"Its available cap space and we can take advantage if Nathan is unable to play," said Maple Leafs senior vice president of hockey operations Dave Nonis. "If he is available to play, Nathan is a world class player."
- Molly Geary