FC Cincinnati head coach Ron Jans just resigned after a player complained he used the n-word out loud in the team's locker-room.

The player filed the complaint with the Major League Soccer Players Association -- which notified FC Cincinnati team officials ... and an investigation was conducted.

Jans has admitted he used the n-word in the locker-room but insists he wasn't trying to attack anyone ... he was simply singing along with a song that was playing.

And no, we don't know which song he was singing along with (we're curious too).

Jans spoke with the Cincinnati Enquirer about the incident and when asked if he has any regrets about the way things went down, he gave this response ...

"I wouldn’t have sung the word, that’s for sure. I learned that lesson. But I am who I am and if it doesn’t fit in this locker room, I think for a lot of players it was a good match and sometimes an excellent match but not with all of them."

There are also allegations Jans made insensitive comments about slavery during a team trip to Washington D.C.

Jans was initially suspended pending the results of the investigation, but club president Jeff Berding announced Tuesday the coach has officially resigned.

“As Major League Soccer’s investigation unfolded and some themes emerged, Ron offered his resignation and we agreed that it was the best course of action for everyone involved with FC Cincinnati,” Berding said.

“We place the utmost importance on a strong culture within our club, beginning in our locker room, and that every person connected with FC Cincinnati feels valued, respected and trusted."

The statement continued ... "Racial and cultural diversity is a major part of what makes the game of soccer so special, and we place the highest priority on respecting every person involved in our game."

"This includes absolutely everyone associated with our club, from our locker room and front office, all the way through to our fans."