"Brian Williams, that's one," Coughlin said, hinting that the team could sign another cornerback. "He's a veteran, he knows how to play, he has been a good, physical blitzer. We needed somebody who can learn some things real quick and go from there."
Cornerback Dre' Bly also worked out for the Giants, according to the Newark Star-Ledger.
The Giants waived linebacker Kenny Ingram to make room for Williams on the roster.
The Giants have already lost three cornerbacks for the season in camp, including Bruce Johnson, who ruptured his Achilles early in camp.
First-round pick Prince Amukamara remains out with a broken foot.
The 5-foot-11 Williams, 32, was Atlanta's third cornerback last season. Williams suffered a left knee injury in the Falcons' season finale against the Carolina Panthers and missed the NFC divisional playoff game against the Green Bay Packers. He had 36 tackles and one sack last year.
Williams, who has 19 career interceptions, played in just five games in 2009 before undergoing reconstructive surgery on his right knee.
Ohm Youngmisuk covers the Giants for ESPNNewYork.com.