Collins, a nine-year NFL veteran, stopped reporting to practice before Week 3 as the Lions searched for suitors. Campbell said last week that he met with Collins to communicate their plans to deal him, but the franchise ultimately couldn't reach an agreement with another team.
"We've been through two games now and you make your assessment and your judgement after two games and that's where we're at," Campbell said of Collins on Thursday. "There again, we felt like it was, if you're going to grow and you're going to try to get better as a team, as a unit, everything, you better do it now.
"I think this is best for Jamie as well. He gets a chance to go somewhere and do what he does and we're just in a different place."
The 31-year-old Collins can sign with any team immediately. He is making a fully guaranteed $8.8 million from the Lions this season.
Collins, a one-time Pro Bowl selection, recorded 10 total tackles and a fumble recovery in two games for the Lions this season.