Newman will miss at least one game and could be sidelined for Cincinnati's remaining three regular-season games, according to sources.
During his news conference earlier Monday, coach Marvin Lewis was vague in discussing Newman's injury. He told attending reporters only, "he's a little sore."
It certainly appeared Newman had a more significant injury than minor soreness.
Immediately after Sunday's 42-28 victory over the Indianapolis Colts, Newman was given a leg brace and crutches. During Monday's open locker room period, the veteran cornerback was still sporting the stiff leg-length brace and crutches.
The AFC North-leading Bengals (9-4) have been depleted by injuries on defense. Star tackle Geno Atkins and top cornerback Leon Hall headline a list of key defensive players Cincinnati has placed on season-ending injured reserve.
Newman, 35, has started all 13 games this season, his second with the Bengals. The two-time Pro Bowler has 52 tackles and two interceptions.
Newman left Sunday's game in the middle of the fourth quarter. Slowly walking on his own power, he left for evaluation for what was classified as a left knee injury.
The Bengals expect to replace Newman with second-year cornerback Dre Kirkpatrick. Because of the injuries to Hall and others, Kirkpatrick has had more extended playing time in recent weeks playing as a slot cornerback in nickel situations.
"Terrence and Leon and Adam [Jones] have been able to hold Dre at bay," Lewis said. "They've had a big stiff-arm on him in trying to keep their jobs from him. Frankly, they've been great mentors for him. He'll get an opportunity to expand his role."
Jones has one message for Kirkpatrick: study.
"When you're starting, you got to do a lot more studying," Jones said. "It's not like you're just playing a couple plays. It's different when you're out there playing the whole game. I'll be on him, because we can't let down in the back end. We're playing too good right now to have any lag in the back end."
The Bengals could be without another defensive back this week, as well. Safety George Iloka left in the second half Sunday with a head injury. Lewis said Iloka is going through concussion protocol and that a determination on his status will come later in the week.