Henry suffered the season-ending injury during a drill, going down untouched while running downfield, a source told ESPN's Adam Schefter. He will have a second opinion Wednesday, the source said.
It's a significant loss for the Chargers, who was set to assume the main pass-catching role with Antonio Gates not on their roster for the first time since 2003.
Henry had 45 catches for 579 yards and four TDs in 2017, his second season out of Arkansas. He averaged 12.9 yards per reception last season, the third-most among tight ends behind only Rob Gronkowski (15.7) and Vernon Davis (15.1).
Gates, meanwhile, remains unsigned.