Karlsson was not completely healthy but played against Nashville on Tuesday and should have felt even worse when he played 22 minutes against Chicago on Thursday.
"He played in Nashville, obviously not 100 percent, and he was definitely not 100 percent in Chicago," coach Bob Boughner told local media.
"We had to make that decision, to kind of shut down over the weekend and get him back home, to let the medical team at home check him out," Boughner said.
Karlsson has struggled with injuries during all four seasons in San Jose.
On January 24, he underwent surgery for a muscle injury to his left forearm and missed 15 games in six weeks.
"At this point in the season, we do not want to put a guy like (Karlsson) in a risk situation where it will be a bit more dangerous," said Boughner.
San Jose has already lost out on the chance to reach the Stanley Cup playoffs.
It has given some hope that the Swede could be at the World Cup in Finland in May.
But yesterday's message may put a stop to it depending on how seriously injured he is.