Speaking to TMZ Sports about Kaepernick, Williams said the former San Francisco 49ers quarterback should "go do something else" if NFL teams have decided they don't want to give him a chance to play.
"I'd rather be somewhere I'm celebrated rather than where I'm tolerated," Williams said.
Williams had his own unique relationship with the NFL. He retired from the league after the 2003 season at the age of 27 as a member of the Miami Dolphins, returned the following year and was suspended for the entire 2006 season for a fourth violation of the substance-abuse policy.
The 1998 Heisman Trophy winner wound up playing for the Dolphins and Baltimore Ravens from 2007-11 before retiring for the final time in Feb. 2012.
Kaepernick has been out of the NFL for 10 months, playing his last game as a member of the 49ers on Jan. 1 in the 2016 regular-season finale against the Seattle Seahawks. He opted out of his contract with the team two months later, becoming a free agent.
After going unsigned by a team, Kaepernick filed a collusion lawsuit against the NFL owners in October.
A second-round pick by the 49ers in 2011, Kaepernick played six seasons in San Francisco and was the team's starting quarterback in Super Bowl 47 against the Ravens.