The United States are hoping to have Jozy Altidore back from his hamstring injury for the knockout stage match against Belgium.
"We are very optimistic. Every day's a big step forward with Jozy," said Jurgen Klinsmann.
The United States don't have a similar option to Altidore as a reserve, so they have been playing with Clint Dempsey up front.
Altidore was spotted running during the United States' training session on Friday.