Mike Ditka's not lightening up on NFL players who don't stand for the national anthem ... unless calling them disrespectful troublemakers nobody will remember is considered lightening up.

TMZ asked Da Coach how he feels about anthem protests on the 16th anniversary of 9/11.

Iron Mike concedes players have the right to do what they want to do ... but thinks 9/11 is different and believes most will stand for Old Glory.

As for the "malcontents" ... Ditka says just let them be and move on -- they'll be forgotten.

He's come a long way since wanting to kick them out of the country.

Read more from TMZ

Photo: Getty Images