Four years after launching the protest movement that effectively ended his career, the verdict is in.

Colin Kaepernick took a knee on the right side of history.

From being widely vilified for kneeling during the US national anthem to protest racial injustice and police brutality, the former San Francisco 49ers quarterback now stands vindicated.

The surging currents which have carried the Black Lives Matter movement into the mainstream of American life have also forced many of Kaepernick's critics to reverse course.

Across the NFL, players hitherto leery of speaking out are now stating their determination to kneel in solidarity with Kaepernick this season.

At the pinnacle of the NFL, Commissioner Roger Goodell has encouraged teams to consider hiring Kaepernick, admitting that the league botched its initial response to the quarterback's protests.

And even President Donald Trump, who once suggested Kaepernick should "find a country that works better for him" and that players taking a knee were "sons of bitches" who should be fired, now believes the quarterback should "absolutely" be given anther chance in the NFL.

So will the clamour to see Kaepernick restored to the NFL lead to a comeback? The jury remains out.

While there is undeniable momentum for a Kaepernick resurrection, a return may not be as straightforward as it seems.

Kaepernick, 32, has not played a down in the NFL since January 1, 2017.

Returning to the sport after a near four-year layoff would be virtually unprecedented.

From vilified to vindicated: what next for Colin Kaepernick?
From vilified to vindicated: what next for Colin Kaepernick? GETTY IMAGES NORTH AMERICA / EZRA SHAW

In recent history, only Michael Vick, who joined the Philadelphia Eagles in 2009 after serving a two-year prison sentence for running a dog-fighting ring, is comparable.

Vick, who was 29 at the time, made only one start for the Eagles that year as he readjusted to life in the NFL. A similarly arduous rehabilitation could be expected for Kaepernick.

"Three full seasons is an interminable break from the game, and Kaepernick would have to be, at best, a backup and maybe even, gulp, a third-stringer," NFL Network analyst Judy Battista said.

"I don't know what he can offer in terms of current ability to win games -- how can anybody? The only way to find out is for a team to bring Kaepernick in for a legitimate workout."

Drew Rosenhaus, an NFL super agent who represents more than 170 players, is adamant Kaepernick will find a team.

"I think he should get signed. I think he will get signed," Rosenhaus said.

"Bring him to training camp and give him a chance to compete like everybody else. He deserves that.

"If he is not good enough on the football field -- we'll never know unless he gets a chance."

The NFL has already extended an olive branch once before to Kaepernick, who reached a settlement with the league last year after filing a grievance alleging NFL owners conspired to keep him out of the league.

Kaepernick's kneeling protest has been adopted around the world during demonstrations against racism and police brutality
Kaepernick's kneeling protest has been adopted around the world during demonstrations against racism and police brutality POOL / CARL RECINE

Last November, the NFL organised a workout for him in Atlanta, inviting all 32 teams to send representatives.

Kaepernick eventually withdrew 30 minutes before the start of the workout after complaining about the exclusion of media and the terms of an NFL liability waiver.

Although Kaepernick subsequently held an open practice in Atlanta, where reports suggested he looked solid enough to be a realistic backup option, the acrimony surrounding his aborted NFL-backed workout suggested any chance of a return to the league remained remote.

The tumultuous events since the May 25 death of unarmed black man George Floyd during his arrest by police in Minneapolis however radically altered the landscape.

Taking a knee has become a ubiquitous emblem of protests which erupted across the world, a commonly understood way of demonstrating against racism and police violence.

In recent weeks, NFL coaches have recently lined up to sing Kaepernick's praises.

Seattle Seahawks coach Peter Carroll now says he regrets not signing Kaepernick in 2017, and hailed the quarterback for taking a "courageous" stand.

"We owe a tremendous amount to him for sure," Carroll said.

Los Angeles Chargers coach Anthony Lynn, meanwhile, said teams would be "crazy" not to consider working out Kaepernick.

"I haven't spoken with Colin, not sure where he's at as far as in his career, what he wants to do," said Lynn, one of only three black coaches in the NFL.

The proof of the pudding, as far as Kaepernick is concerned, will be in the hiring. So far, for all the positive comments, no team has taken the next step of offering Kaepernick a workout.

Sports Illustrated NFL writer Jenny Vrentas questioned whether coaches like Lynn were truly serious about giving Kaepernick a chance to rebuild his career.

"With Anthony Lynn's comments you're kind of having it both ways a little bit," Vrentas told Sports Illustrated's MMQB podcast. "You're saying that we would of course consider him -- but at the same time no steps have been taken.

"I think we need to see more and expect more out of the teams. If they aren't bringing him in for a workout tell us why."

Adding to the uncertainty is the desire of Kaepernick himself.

After last November's workout Kaepernick insisted he had been "ready for three years" to return, and called on the NFL's teams "to stop running from the truth."

The quarterback has remained mostly silent about his intentions since then.

If no team signs Kaepernick as a player, it may be that his future lies in activism.

On Thursday the online publishing platform Medium announced it had signed Kaepernick to create stories focused on race and civil rights.

NFL chief Goodell, meanwhile, has acknowledged the league would welcome Kaepernick's involvement as an advisor on social issues relevant to the league.

"If his efforts are not on the field but continuing to work in this space, we welcome him to that table and to help us, guide us, help us make better decisions about the kinds of things that need to be done in the communities," Goodell said.