The Seahawks signed Brock, 29, to a one-year deal on Aug. 16, and he was immediately thrown into the competition at cornerback. Brock was seen as an option on the outside or working as a slot cornerback. But Seattle opted to stay in-house with its options and will go into the regular season relying on veteran Jeremy Lane and rookie Shaq Griffin opposite Richard Sherman.
Brock's late signing was due to off-field troubles. He was charged with felony domestic violence in June, but those charges were dismissed in August by the Santa Clara County district attorney's office.
Brock started 31 of 32 games over the past two seasons for San Francisco before his release in April.
Brock still could face discipline from the NFL under the league's personal conduct policy, even though the district attorney's office dismissed the case against him based on insufficient evidence because the alleged victim -- who is the mother of his children -- declined to cooperate.
Shortly after the charges against Brock were dismissed, the woman's attorney wrote in an open letter: "My client's choice not to testify was voluntary and not dependent upon past or future actions by any part. She has indicated to me that this was a verbal altercation. She and Mr. Brock look forward to co-parenting their two young children."
Brock told reporters after signing with Seattle that he's confident that "nothing will happen" with regards to league discipline.
Brock's agent, Ron Slavin, told Seattle reporters the same day: "I can't ever predict what they're (the NFL) going to do. I know with the information we have and the things in writing and the things that she's already admitted, I know he's going to cooperate, I'm going to be a part of it, I know she's going to cooperate, so I'm hoping there won't be."
Brock's base salary on his one-year Seahawks deal was $900,000, the minimum for a player with his experience.
Brock's trade to Minnesota marks another change in Seattle's cornerback depth. Seattle lost DeAndre Elliott to a broken ankle in the team's final preseason game Thursday night and acquired Justin Coleman in a trade with the New England Patriots earlier Friday.
The trade was first reported by NFL Network.
The Associated Press contributed to this report.