It wasn't immediately clear when Josefson was hurt during Tuesday 3-1 win over the Islanders. He played six shifts in the first period and two more in the second, but didn't return to the ice for the third.
The Devils, who will begin the Stanley Cup playoffs next week, announced the injury during the third period.
"Everybody in the room really feels for Jake," Devils goalie Johan Hedberg said. "He's been through so much these two years with injuries and every time he is getting his groove and things are going well for him, and it looks like he is really to take the next step, some unfortunate injury happens."
Josefson broke his right collarbone on Oct. 21 and missed 37 games. The second-year player has two goals and seven assists in 41 games this season.
Information from The Associated Press was used in this report.