Bruce Jenner's Olympic Teammate -- "It's Courageous ... But I Don't Get It"

Caitlyn Jenner's former decathlon teammate -- who competed for Team USA with Bruce in the '76 Olympics -- says he's struggling to "compute" the whole Jenner situation ... but still considers her a friend.

TMZ Spoke with Fred Dixon ... who reunited with "Bruce" at his 64th birthday party last year (a reunion featured on "Keeping Up with the Kardashians").

Dixon was extremely honest when we asked if he'd seen the new cover of Vanity Fair .... saying, "Bruce was one of the best athletes who ever existed. Now, to see that photo ... somehow it doesn't compute."

"I look at it and I don't understand it. I'm not in any way judging him ... but it's very different."

For the record, Jenner told Diane Sawyer he expected some of his old friends to feel this way ... and understands -- "Some people will get it, some people won’t get it, it’s OK."

As for Fred, he says the bottom line is simple -- "The soul that was and is Bruce Jenner is still my friend. I don't understand what's going on now ... but he's still my friend."