Multiple sources also expressed doubt that Brown would ever kick again in the NFL after documents surfaced this week in which the veteran kicker admitted to domestic abuse against his wife.
NFL senior vice president Adolpho Birch, in a letter sent to Brown, said the league wants to investigate further upon learning of the new documents, which were released by the King County (Washington) Sheriff's Office and stem from Brown's 2015 arrest.
"As you may be aware, the NFL made multiple requests of the Sheriff's Office for any and all pertinent information developed through its investigation," the letter to Brown stated. "Because the Sheriff's Office was treating its investigation as an open matter, however, the NFL's requests were rejected and the materials first became known and available to us at the same time they were released publicly.
"The released materials appear to contain information regarding other incidents of abuse separate from the May 22, 2015 incident for which you were disciplined under the Personal Conduct Policy. As a result, further investigation by the league into those separate incidents is needed."
In an interview with BBC Sport, NFL commissioner Roger Goodell said, "We take this issue incredibly seriously. This is something we've been working on with policy changes, to educating our players to make sure they understand how they deal with issues with their family, give them resources to be able to deal with this. But when it happens, we're not going to tolerate it. So we have some new information here, we'll evaluate that in the context of our policy, and we'll take it from there."
Brown already served a one-game suspension without pay to kick off this season for violating the league's personal conduct policy.
Asked whether Brown can expect further punishment, Goodell told BBC Sport, "The policy the way it's structured right now is for an incident. And it can be reduced or increased on the basis that first offense is six games, second offense is banishment. So it's the only policy, the only issue where we have that type of penalty."
Birch's letter to Brown said the NFL expects "to conduct this review expeditiously and make any appropriate adjustments to your roster status in a timely manner."
By being placed on the commissioner's exempt list, Brown, who has three days to appeal the decision, will still be able to collect his base salary of approximately $1.15 million and is permitted to attend the Giants facility "for meetings, individual workouts, therapy and rehabilitation, and other permitted non-football activities," the letter said. He is not allowed to attend practices or games.
"We're not going to turn our back on Josh," McAdoo said as he was being peppered with questions. "He's our teammate."
McAdoo said he went to each position room Thursday to inform players that Brown would not make the trip to London. The Giants left Thursday evening. Former Bears kicker Robbie Gould has signed a prorated one-year deal and will join the team Saturday in London.
ESPN staff writer Jordan Raanan contributed to this report.