United States attacker Giovanni Reyna said he is "100 percent" healthy despite being an unused substitute in the team's 1-1 draw with Wales to open the World Cup.

Reyna, who has battled injuries for most of the last year, featured in Borussia Dortmund's final three games before the World Cup break and figured to be a major contributor for the US at the tournament.

"I feel really good. I feel great," Reyna said. "I feel fine. [Coach Gregg Berhalter] doesn't have to tell me why he didn't put me in or why he does."

Berhalter used his first four substitutes to insert midfielder Brenden Aaronson, striker Haji Wright, right-back DeAndre Yedlin and midfielder Kellyn Acosta all with the US leading 1-0. He appeared to be ready to sub in center-back Aaron Long before Wales equalized through a Gareth Bale penalty in the 82nd minute.

Despite Reyna's claims of full health, Berhalter, who brought on Jordan Morris for Timothy Weah in the 88th minute, said he was taking a cautious approach.

"It was trying to get him up to speed. I think there was a little bit of tightness that we were guarding him against in Al-Gharafa in the training exercise as a precaution." Berhalter said. "But we've been building him up and think he can play a big role in this tournament. The question is when. Hopefully Friday, he'll be another step ahead."

The US has three days off before it takes on group-leader England on Friday after the Three Lions opened their tournament earlier on Monday with an emphatic 6-2 win against Iran take control of Group B.