Karlsson is in Sweden participating in the country's pre-Olympic camp.
"I'm sure I'll be able to skate 100 percent when the season starts," Karlsson told Swedish reporter Marie Lehmann, according to the Senators website. "This summer [has] been my best so far, workout-wise."
Karlsson's left Achilles was torn 70 percent by the skate blade of Pittsburgh Penguins forward Matt Cooke during a game Feb. 13. Karlsson had surgery but was able to return to action on April 25, playing in three regular-season games prior to participating in 10 Stanley Cup Playoff games.