Bowe Bergdahl will return back to the United States on Friday after undergoing medical treatment at a military hospital in Germany, a U.S. defense official said on Thursday.

The American soldier, who was released by Afghan insurgents in a swap with the Taliban, is "expected to arrive on Friday" at Brooke Army Medical Center in San Antonio, Texas, a U.S. defense official, who spoke on condition of anonymity, told Agence France-Presse.

On May 31, Bergdahl was handed over by insurgents in eastern Afghanistan. For more than a week, he has been recuperating at the Landstuhl Regional Medical Center in Germany after he was flown to Bagram Airfield.

"In return for Bergdahl's release, the United States transferred five Taliban detainees held at Guantanamo prison to Qatar, in a deal that has sparked intense criticism in Washington," AFP reported. "Bergdahl has yet to speak to the news media about his nearly five-year ordeal and Pentagon officials have said his health has been steadily improving in the days since his release."

"His disappearance from a base in eastern Afghanistan in 2009 has prompted speculation that he deserted his post before he was captured."

On Wednesday and Thursday, Bergdahl's letters and other correspondence emerged suggesting a troubled state of mind during his deployment. It is also being insinuated that he lacked confidence in his commanders.

"Leadership was lacking, if not non-existent," he wrote in a letter sent to family during his time in captivity, obtained by the Daily Beast.

The letter, one of two sent to his family via the International Committee of the Red Cross, was marked by numerous spelling errors.

"The conditions were bad and looked to be getting worse for the men that where actuly the ones risking thier lives from attack," he wrote in a March 23, 2013 letter.

He also seems to be trying to appeal for understanding over his disappearance, though he does not explicitly state that he deserted, AFP reported.

"If this letter makes it to the USA, tell those involved in the investigation that there are more sides to the cittuwation," he wrote.

"Please tell D.C. to wait for all evadince to come in."

Copies of the two letters were passed to the website by sources in contact with the Taliban, the Daily Beast said.