Karlsson, who won the Norris Trophy voted as the best defenseman in the NHL in 2012 and 2015 while playing for the Ottawa Senators, sustained a lacerated Achilles tendon in 2013 and a foot injury in the 2017 playoffs that required surgery.
"This is the first time with the groin," said Karlsson, who was traded to San Jose last Sept. 13. "I don't know what happened, but the other ones there's nothing I could have done about it. It's not something that I worry too much about."
The 29-year-old has been skating for two and a half weeks and took part in an informal scrimmage with Sharks teammates in San Jose on Thursday, the website said.
"Honestly, it probably felt pretty good sooner than I expected, but I still took the appropriate time that the surgeons wanted for it to be healed," Karlsson said.