Here's the deal ... 19-year-old Quinn Simmons -- a rising star in cycling -- commented on a Dutch journalist's social media post Wednesday, showing his support for POTUS.

In the original post (which has since been deleted) ... the journalist wrote, "If you follow me and support Trump, you can go. There is zero excuse to follow or vote for the vile, horrible man.”

Simmons responded by writing, "Bye" with an emoji of a dark-skinned hand waving. The cyclist later told a commenter "That's right" after the person had called him a "Trumper."

Turns out, Simmons' racing team -- Trek-Segafredo -- didn't like the exchange one bit ... and hit him with an indefinite ban.

But, the team says the punishment was NOT for Simmons' pro-Trump political views ... but rather, they say they just didn't like the way he went about expressing them.

"He was suspended for engaging in conversation on Twitter in a way that we felt was conduct unbefitting a Trek athlete," the team said in a statement.

Added the team's manager, Luca Guercilena ... "We hold all Trek staff and management to a high ethical standard and our athletes are no exception."

For his part, Simmons released a statement on it all ... writing, "As an American rider, I have always been proud to represent my country. Riding for an American team has been a lifelong dream. A big reason I chose this team was because of the American values behind it."

Simmons continued, "To those who found the color of the emoji racist, I can promise that I did not mean for it to be interpreted that way. I would like to apologize to everyone who found this offensive as I strongly stand against racism in any form."