The young American striker is now likely to miss out on the USA's Hexagonal matches against Costa Rica and Mexico in September.
Boyd sustained the injury while with the U.S. national team this week. The Yanks defeated Bosnia-Herzegovina 4-3 in a friendly on Wednesday, but Boyd did not take part in the match.
The 22-year-old striker is off to a strong start with the Austrian Bundesliga club this season, with three goals in all competitions so far.
The injury puts Boyd's status in doubt for the USA's two World Cup qualifiers in September: Sept. 6 at Costa Rica and Sept. 10 versus Mexico.