Aron Johannsson's ankle injury wasn't suffered during the U.S.'s World Cup campaign, according to AZ's Earnie Stewart. Robert Cianflone/Getty Images

United States international Aron Johannsson had ankle surgery on Tuesday and his club, AZ Alkmaar, expects the 23-year-old to be back on Sept. 1, team director Earnie Stewart told ESPN FC.

Johannsson's injury wasn't picked up during the Yanks' World Cup in Brazil but was an long-term injury that the striker wanted to address, Stewart clarified.

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"He's had this injury for a longer while than at the U.S. national team," Stewart said in an telephone interview. "It was something that you could play with; it wasn't a problem to. I've played with the same problem myself. Once it's time to rest, it's something that can aggravate you every time you step out on the field."

While the team director, a former U.S. international himself, wouldn't reveal the extent of Johannsson's injury, he is optimistic that his forward will be ready to play before AZ's game against Heerenveen on Sept. 13.

Johannsson is AZ's lead striker, with the Icelandic-American scoring 17 goals in Eredivisie last season. He took the starting role after Jozy Altidore moved to Sunderland, and Stewart also reflected on the current struggles of his former top hitman.

Jozy Altidore 'has to make it work in Sunderland'

Altidore, 24, had a rough debut season with Sunderland last year, scoring twice in 38 appearances. Before Altidore picked up a Grade 2 hamstring tear against Ghana in the Americans' opening game of the World cup, there were plenty of speculation that the hulking striker could use the tournament as a platform to exit the Black Cats. Rumors spoke of a return to the Dutch league, another European league or even MLS considering the recent arrivals of Michael Bradley and Clint Dempsey.

However, Stewart -- a former U.S. international and mentor to Altidore during their two years together in the Netherlands -- believes Sunderland is where the Yanks' attacker should look to succeed.

"First of all, he has to make it work in Sunderland," Stewart insisted. "I believe that he has the quality as a player to become a very important part of Sunderland and be something in English football.

"Otherwise, he's going to be known as the player who was at Hull and didn't pan out and now is at Sunderland and didn't pan out. I'm not Jozy, but I wouldn't go back to MLS right now [if I were in his shoes]. Because I think he's a very good player."

Earnie Stewart believes that Jozy Altidore should remain at Sunderland and prove himself. Ian Horrocks/Getty Images

Stewart also said he believes Altidore's poor statistical production wasn't solely his fault. He pointed to the way that the relegation-threatened club played last season and explained that there weren't many opportunities for any striker to score in that system.

"A forward in England most of all is looked upon to score goals. If it doesn't happen after a few weeks then in [their opinion] you haven't done well. But that means nothing to me," he explained. "Obviously, you want your center forward to score, but depending on the way that a team is playing, the style, where you have pressure or don't and how the support is, determines whether he's going to score goals or not."

Jurgen Klinsmann's solid plan

Stewart also took some time to praise Klinsmann's work with the national team this summer in Brazil. Despite the U.S. manager coming under some criticism for not playing the imposing, attacking style that he promised when taking the job in 2011, the AZ executive believed that Klinsmann managed the club effectively considering all of the circumstances involved.

"Tactically, in the way they lined up, I don't see any faults in that," Stewart said. "I truly believe that he did a fantastic job with the national team especially in the group that he was in."

Stewart also defended the U.S. manager's decision to focus on playing counter-attacking football, especially considering the conditions in Brazil.

"You can't play high pressure to a team for 90 minutes in that weather. That humidity that was in Brazil, I think it would've been suicidal to do that," he said.

"In retrospect, all of the teams that were more defensive-minded, who were more defensively sound, and played counter-attacking football, all made it pretty far in the tournament."

Hope for Freddy Adu's future

While Stewart was able to revitalize Altidore's career in the Netherlands, he wasn't able to find the same success with recent AZ trialist Freddy Adu.

Stewart played with Adu at D.C. United in his rookie season in 2004 and wanted to give him a chance to showcase his talent at Alkmaar. Adu was fit and showed some positive signs but wasn't able to find a fit into AZ's tactics and the club ended his trial, continuing a troubling free fall for the one-time promising U.S. starlet. One area of concern appeared to be the now 25-year-old's lack of development since his days as a teenager in MLS.

"Not so much difference from then," Stewart said. "He still had all of the same things he was able to do back in the day. Obviously, he's a bit older and more comfortable on the ball but I can't say that it's totally different from back then."

Now, with Adu still searching for his 10th club, there is concern that his time as a professional player might be coming to an end. Stewart disagreed and said he believes Adu could find a fit on a team in the Netherlands, though he also acknowledged past mistakes are affecting the midfielder.

"I think a lot of [Adu's struggles to find a club] has to do with his past," he said. "Once you're way down in life and especially in soccer life, the choices that you made at an early stage are very important."

He added, "I don't believe that back in the day, all of the choices that were made were in a sportly matter. Making sure that you develop yourself and everything. That might be one of things that's held against him right now. And its difficult now that he's 25 to go back and re-track all of that in-development."