USA forward Clint Dempsey has acknowledged that his side face a "very difficult game" against Portugal in their crucial Group G clash.

Victory for the United States in tonight's encounter in Manaus will ensure their passage through to the next round, but they come up against a Seleccao side looking for redemption following their heavy 4-0 defeat against Germany last time out.

"In an ideal world, if you get the three points [against Portugal] then we will be able to go through the group, but that is easier said than done," Dempsey, who scored his side's opening goal against Ghana, told FIFA.com. "It's going to be a very difficult game, we will have to be at our best to get the points."

Dempsey made his international debut in 2004 and has gone on to make over 100 appearances for the US.