Cowboys executive vice president Stephen Jones told reporters at the owner's meetings in Orlando, Fla., that Williams was injured but did not disclose the nature of the injury.
According to the Dallas Morning News, Williams underwent surgery four weeks ago.
Williams, 28, has never missed a game since joining the Cowboys in 2013 as a third-round pick from Baylor. In 80 regular-season games, including 66 starts, Williams has 230 receptions, 3,359 receiving yards and 20 touchdowns. He also has eight receptions for 198 yards and three scores in three playoff games.
Last season, he recorded 44 catches for 736 yards and scored five receiving touchdowns.
The Cowboys signed him to a four-year, $17 million contract extension last March with $9.5 million in guaranteed money.