Common to NFL: Don't Blackball Colin Kaepernick, 'This Is America'

Colin Kaepernick has been told flat-out he can't get an NFL tryout unless he quits kneeling ... and Common says that ain't right, especially not in this country.

"This is America so he gotta be free to express himself," the rapper said.

"You gotta allow human beings to be human beings ... they express themselves and then go play the game."

TMZ Sports broke the story ... the Seahawks straight-up 86'd a planned workout with Kaep 'cause he refused to stop his kneeling protests.

Common says he gets why NFL teams are requesting that Colin stand -- they got a business to run -- but it's still a damn shame that's the only reason "a great quarterback" can't do what he loves.

"Hopefully ... Kaepernick will make his choice and he'll be able to play in the league."