"We don't do that in the United States," Hagel told reporters at a NATO defence ministers meeting. "We rely on facts."
Hagel said the Army will review the circumstances surrounding how Bergdahl left his unit and was captured by the Taliban, and added, "It's not my place as a former sergeant in the Army to decide who's worthy of being a sergeant and who isn't."
Bergdahl was released Saturday from five years' captivity by the Taliban in exchange for five top Taliban officials.
Men in Bergdahl's unit have said that some did die in the efforts, even if indirectly.
"Those soldiers who died on those missions, they would not have been where they were ... If Bergdahl had never walked away," said Evan Buetow, a sergeant in Bergdahl's unit at the time. "At the same time I do believe it is somewhat unfair for people to say, 'It is Bergdahl's fault that these people are dead.' I think that's a little harsh."
Congressional hearings and briefings are looking into the deal that swapped Bergdahl for Taliban officials who had been held at Guantanamo Bay, Cuba, and several lawmakers said President Barack Obama didn't notify them, as required by a law governing the release of Guantanamo detainees.
White House staff members called key members of Congress to apologise.
