Despite the fact that Hagel was McCain's 2000 presidential campaign chair and the two are friends, McCain said he has some concerns during an appearance on CBS' "Face the Nation."
"My questions about him -- and they will be raised in the nominations -- are, what is his view of America's role in the world? Whether he really believes that the surge was the worst blunder since the Vietnam War. That clearly is not correct; in fact, it's bizarre. Why would he oppose calling the Iranian revolutionary guard a terrorist organization? [It's the] same outfit that's on the ground now in Syria killing Syrians, same outfit that was exploiting the most lethal IEDs [improvised explosive devices] into Iraq killing Americans," McCain said.
"So these are legitimate questions that need to be asked," he added. "I honor his service. We are friends, but I have an obligation to the men and women who are now serving in uniform."
McCain also voiced concerns about the nomination of John Brennan as CIA director. He pointed to what he called discrepancies in Brennan's views on torture and his possible role in information leaks after the killing of Osama bin Laden.
Notable deaths of 2014 [PHOTOS]