Raheem Sterling says it is a "real disappointment" that some England fans have not understood why players are taking the knee and booed the gesture.
The rearranged European Championship is just days away but the negative reaction from some to the group's anti-racism stance has dominated much of the build-up.
Jeers were drowned out by applause when players took the knee before England faced Austria last Wednesday – their first international match in front of fans in 18 months.
Gareth Southgate spoke to his players about the incident ahead of Sunday's return to Middlesbrough to take on Romania, telling the media the group "feel more than ever determined to take the knee" at Euro 2020.
England players received the adverse reaction their manager predicted when they made the gesture again on Sunday, which frustrated forward Sterling.
"Honestly, it's something I didn't even really want to speak on," he told talkSPORT. "But, yeah, it's just how can I say... if you can't understand the meaning behind it and the cause behind it, then it's a real disappointment to see that.
"But I don't really even want to go into it too much, to be honest with you."
Sterling watched from the stands as some supporters jeered players, with Luke Shaw among those booed for kneeling in pursuit of equality.
"It's really simple," the England left-back said. "I think Jord (Jordan Henderson) said it the other day.
"We've had discussions about it, we've all chosen what we wanted to do, we all agree it was the right thing to do to carry on taking the knee and it's as simple as that.
"We'll keep doing that and we believe in that and we won't stop."
