The United States international has suffered a microfracture and bone oedema in his right tibia and fibula following his side's last-16 defeat to Belgium, an injury confirmed after medical tests.
The incident occurred in the 52nd minute when the winger struck the leg of Youri Tielemans while attempting a shot. He tried to continue despite discomfort but was substituted a few minutes later by Mauricio Pochettino.
The United States Soccer Federation confirmed the diagnosis in an official statement, reporting a microfracture and bone oedema in the tibia and fibula of his right leg.
Although his World Cup campaign is now definitively over due to elimination, the injury remains a concern for AC Milan ahead of the new season.
Pulisic is expected to miss several weeks but could return in time for the Serie A opener against Torino on 23 August.