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.
The 23-year-old 2012 Norris Trophy winner finished with seven goals and 15 assists in his 27 games one season after leading NHL defensemen with 78 points (19 goals) in 81 regular-season games.
"The normal feeling isn't there, but I'm getting used to not normal," Karlsson told Lehmann.
Karlsson's foot remains numb due to some missing nerves.
"It's not really connecting down there," he said.
Karlsson played more than 25 minutes in seven of the 10 playoff games, including 39:48 in a two-overtime win against the Penguins on May 19.