(Reuters) - United States coach Juergen Klinsmann has told his players to get their families to change their return flights from Brazil until after the World Cup final.

The U.S. face Belgium in the second round of the World Cup on Tuesday after emerging from a tough Group G ahead of Portugal and Ghana.

Defender Omar Gonzalez says Klinsmann's upbeat assessment of his team's chances of progressing has even gone as far as encouraging revised travel plans.

"Juergen has been nothing but positive. He's telling us, he's telling our families to change our flights to July 14th, 15th, because we're going to be here until the very end," said the center-half.

"So that just speaks volumes to how positive he is, how much he believes in this team, and obviously it trickles down to all of us.

"That means that we're all as confident as he is, and that we all believe in this team. We plan on being here a few more weeks," added Gonzalez.

Klinsmann was criticized by American media prior to the tournament for saying that it was "unrealistic" to talk about the U.S. winning the World Cup.

But now his team are repeating the mantra that in the knockout stage, anything is possible if the Americans can prepare well and play to their potential.

"You get to this part in the tournament and it's clear that (it is about) whoever prepares better, whoever's more committed on the day, whoever makes more plays over the course of 90 minutes, whoever's willing to have a group of guys on the field who fight and are so determined to come off the field a winner," said midfielder Michael Bradley.

"Those are the things that count. So, for us, it's about using the time in between these games to recover, physically, mentally, and know that when we step on the field it's going to be a hard game, one that tests us in every way.

"But like we keep saying we're excited about it and we'll be ready to go," added the midfielder.