UPDATE: The Czech Republic FA has confirmed that they will play the U.S. in Prague, although it will come on September 3. Normally matches are played Friday and Tuesday, but this date will apparently start with a Wednesday match instead.
The United States just finalized its Send-Off Series for friendlies before the World Cup, but they're apparently already working on friendlies for after Brazil. According to reports out of the Czech Republic, as passed along by Steve Goff, the U.S. will play away to the Czechs in a September friendly.
September will be the first chance for teams to play after the World Cup. FIFA eliminated the August international date so a double date, set for September 5 and 9, will be the Americans' first matches of the 2018 World Cup cycle. The Czech Republic are scheduled to play a Euro 2016 qualifying match on September 9.
In 2010, the U.S. played their first post-World Cup match in August, but skipped the September dates. Four years earlier, the World Cup marked the end of the Americans 2006 calendar, but that was because they did not have a manager as the USSF spent months hoping Jurgen Klinsmann would replace Bruce Arena, only to hire Bob Bradley as interim (and later permanent) manager in December.
The Czech Republic plays most of their matches in either Prague or Olumouc so odds are that the reported September match will be in one of those two cities. The Czechs did not qualify for the 2014 World Cup, finishing behind Italy and Denmark in Group B, and have some work to do before Euro 2016 qualifying with the Netherlands and Turkey both in their group.
If the U.S. takes advantage of every available FIFA date prior to the 2015 Gold Cup, they will have eight friendlies before the tournament starts. That doesn't include a presumed January camp for the domestic players and friendlies to go alone with a May/June training camp to prepare for the Gold Cup so they could play as many as 12 matches between September 2014 and the start of the CONCACAF championship in June 2015.