Pulisic has a bone bruise and a microfracture of his tibia and fibula, the U.S. Soccer Federation said Thursday. The diagnosis was made after an X-ray and MRI on Tuesday.
He would not have been able to play during the remainder of the tournament had the U.S. advanced.
Pulisic is expected to resume training before AC Milan's Serie A opener at Torino on Aug. 23.
Pulisic hit a leg of Belgium captain Youri Tielemans while attempting a shot in the 52nd minute of Monday's 4-1 round-of-16 loss at Seattle. He remained in the game but was hobbling and Sebastian Berhalter replaced him in the 59th minute.
Pulisic failed to score in the World Cup, missing one of the Americans' five matches because of a calf injury and leaving two other games early. He has 30 goals in 90 international appearances.
Pulisic, who turns 28 in September, is entering his fourth season with Milan.