The Oakland Raiders coach was asked about his reported $100 million deal with the team -- and while trying to explain his high salary ... he randomly took a shot at Tom Cruise.

Here's the quote from his interview with Peter King ...

"I’m not making $100 million, just so you know. Well, I never thought Tom Cruise, never thought his movies were any good but he’s making plenty of money."

Weird and random Tom Cruise shot -- but alas, there's more.

"There’s a lot of things that I don’t understand. No disrespect to Tom Cruise. I’m sure he’s a great actor. But you know what? You just go about your life as hard as you can. You try to find something you love and you do the best you can at it."

No word on why Jon dragged Tom Cruise into the conversation -- maybe he finally got around to seeing "Rock of Ages" or "The Mummy" ... both trash.

But what Gruden's clearly forgetting in his weird Tom Cruise rant is "Top Gun" and "Jerry Maguire" and "Jack Reacher" (the first one) was actually pretty solid.

And several people in this office are adamant the new 'Mission Impossible' movie was "f**king awesome" and they're actually mad at Gruden for throwing shade.

By the way, Jon Gruden had a cameo in "DRAFT DAY" -- THE WORST FOOTBALL MOVIE EVER MADE!!!