"I don't know what the owners did," Rubio said. "But what is there, 64 quarterbacks in the NFL? There aren't 63 people better than him."
The NFL has 32 starting quarterbacks. Most teams carry at least three quarterbacks on their roster, with at least two active on game day. Kaepernick has not been counted among the league's starters since Jan. 1, 2017, when he took the first snap for the 49ers in a 25-23 loss to the Seattle Seahawks.
He opted out of the final year of his contract two months later, becoming a free agent. Kaepernick, 30, has been linked to the Seahawks, Cleveland Browns, New York Jets, Miami Dolphins and Baltimore Ravens, but remains unsigned.
Kaepernick began his protests against racial injustice and police brutality by sitting on the bench during the national anthem during the 2016 preseason. He was seen sitting again during Week 3 of the preseason after a photo was tweeted out by Niners Nation. Kaepernick later explained the reasoning behind his protest.
He took a knee before the Niners' Week 4 preseason game and continued to do so throughout the season. Many players around the league soon joined Kaepernick in his effort, drawing both support and criticism from onlookers.
In October, Kaepernick filed a grievance against the NFL, accusing the league's 32 owners of collusion.
"If the NFL [as well as all professional sports leagues] is to remain a meritocracy, then principled and peaceful political protests -- which the owners themselves made great theater imitating weeks ago -- should not be punished and athletes should not be denied employment based on partisan political provocation by the Executive Branch of our government," Kaepernick's attorney Mark Geragos said in a statement regarding the grievance. "Such a precedent threatens all patriotic Americans and harkens back to our darkest days as a nation. Protecting all athletes from such collusive conduct is what compelled Mr. Kaepernick to file his grievance."
"Colin Kaepernick's goal has always been, and remains, to simply be treated fairly by the league he performed at the highest level for and to return to the football playing field."
President Donald Trump has been vocal in his disagreement with Kaepernick's stance, both before he was elected and during his tenure in the White House.
"I have followed it and I think it's personally not a good thing, I think it's a terrible thing," Trump said on KIRO Radio in August 2016. "And maybe he should find a country that works better for him. Let him try. It won't happen."
At a White House event Monday honoring Nascar Cup Series champion Martin Truex Jr., Trump said there are thousands of "patriotic Americans" at every Nascar race. He also mentioned that those involved in the sport stand for the anthem. He also addressed Nascar CEO Brian France.
"And I will tell you -- one thing I know about Nascar, they do indeed, Brian, stand for the playing of the national anthem, right," Trump said. "They do indeed. Somebody said maybe you shouldn't say that, that'll be controversial. I said, that's OK, Nascar's not going to mind it at all. Right fellas? They don't mind it at all."
Rubio said he supports Kaepernick's right to kneel, but doesn't "agree with what he did."
"Look I support his right to stand for what he does," Rubio told TMZ. "I don't agree with what he did, but I support his right to do it. But if you are just talking football, there is a dearth of good quarterbacks and ... there aren't 63 better quarterbacks in the world."
"If there is one place there is a shortage, it's quarterbacks. Obviously I don't understand it. It's hard to ... people don't sign people for a lot of different reasons."
A source told NBC Sports' Pro Football Talk that internal franchise documents in the collusion grievance revealed that multiple NFL teams viewed Kaepernick as a starting quarterback in 2017.
Rubio said he believes that a team will sign Kaepernick and he will get another shot "if he wants one."