Stephen A. Smith and Max Kellerman discuss Spike Lee's planned protest in front of the NFL's New York office in support of Colin Kaepernick. (2:16)

Filmmaker Spike Lee is promoting a planned rally for free-agent quarterback Colin Kaepernick.

Lee tweeted an advertisement for the rally, scheduled for Aug. 23 outside the NFL's headquarters in New York. The ad misspells Kaepernick's name, omitting the first "e."

Lee said on Twitter he didn't organize the protest, but that he supports Kaepernick and "his stance on the injustices in the USA."

I Did Not Organize And Set Up This Protest. However I Still Support My Brother And His Stance On The Injustices In The USA — Spike Lee (@SpikeLee) August 8, 2017

Several civil rights groups are organizing the rally.

Kaepernick, formerly of the San Francisco 49ers, became a topic of national conversation last year for choosing to kneel instead of stand for the national anthem, citing police violence and social injustice against minorities. He parted ways with the 49ers in March and hasn't been signed by another team.

New York Giants owner John Mara said Tuesday that he believes Kaepernick will be on a roster this season.

"I think he still has some good football left in him. I agree with that," Mara said on The Michael Kay Show on 98.7 FM ESPN New York. "But obviously there are other issues that go along with him. Is he willing to sit as a backup behind a starter? What's that going to do with your locker room? Your quarterback room? With your offensive room?

"I believe he'll be back in the league at some point this year with a team."

In May, Mara -- whose team has a settled quarterback situation -- said he received plenty of letters from fans about their thoughts on Kaepernick's protest.

"It was a lot. It's an emotional, emotional issue for a lot of people, more so than any other issue I've run into," Mara told The MMQB in May.

Despite the fact Kaepernick is still without a job, Mara does not believe the 29-year-old quarterback is being blackballed.

"Absolutely not. Anybody who thinks there has been any conversations going on among teams about Colin Kaepernick is crazy," Mara said Tuesday. "That just is not the case. I saw a quote, I think it was Steve Ross in Miami said recently: Teams want to win so badly that if they believe a player can help them win, they are going to bring them on. And I think there are certain issues that go along with Colin Kaepernick and that may have scared some teams away.

"But there is absolutely no blackball going on here. I just don't see that at all."

Information from ESPN's Jordan Raanan and The Associated Press contributed to this report.