Philadelphia Eagles quarterback Michael Vick  is promoting his new autobiography, "Finally Free."

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Vick releases a new autobiography

The NFL quarterback spent about 18 months in prison for dogfighting

Since getting out of prison he has tried to rebuild his career and image

CNN  — 

Philadelphia Eagles quarterback Michael Vick canceled a series of book signing dates because of “credible threats,” his book publishers said.

“Despite warnings of planned protests, Vick had hoped to continue with the appearances as planned, bringing his story of redemption and second chance to major markets,” said Worthy Publishing, a Tennessee-based Christian publishing company. “However, once the reported protests escalated into threats of violence against the retailers, Worthy Publishing, Vick and his family, decided to cancel the events.”

Vick, who spent about 18 months in federal prison after pleading guilty to dogfighting charges in 2007, has been trying to turn his life and his image around in recent years.

Vick helps park get a second chance

In September, he continued his rehabilitation campaign by donating about $200,000 for a new football field for a Philadelphia inner-city youth football team. At the time, Vick said the donation was a gift to the City of Brotherly Love for embracing him after the Eagles signed him following his release from prison.

But not all have embraced the new Michael Vick.

The quarterback was set to promote his new autobiography “Finally Free,” but had to cancel upcoming dates across the country after threats to Barnes & Noble Booksellers and an independent bookstore in New Jersey.

“It is disturbing that a few extremists would threaten Vick’s family and store employees,” said Vick’s spokesman Chris Shigas. “Michael Vick has millions of fans and has countless letters from teachers thanking him for inspiring students to make positive change.”

Last year, Vick announced he had gotten a dog for his family in an effort to show his children how to have a healthy relationship with animals.

“This is an opportunity to break the cycle,” Vick said in a statement in October. “To that end, I will continue to honor my commitment to animal welfare and be an instrument of positive change.”

CNN’s Sarah Hoye contributed to this report