Alvin Porter, the Ravens' second-year cornerback out of Oklahoma State, will start Sunday against the Cincinnati Bengals if Chris McAlister's hurting ankle doesn't allow him to play.

That will not mean, however, the Ravens want Porter to fill McAlister's role. Few defensive backs can.

"What Chris did week in and week out was take the best receiver and actually shut him down," secondary coach Donnie Henderson said. "The guys learned from watching him play hard. That's the thing we are going to miss. We would match Chris up on their best guy."

Neither Porter nor fellow starting cornerback Gary Baxter will shadow the Bengals' Chad Johnson, who leads the team with 348 yards receiving, and veteran James Trapp will continue to serve as the nickel (fifth) defensive back.

McAlister sprained his ankle early in the fourth quarter of Sunday's 20-17 loss in Atlanta. Porter filled in the rest of the game, and a key fourth-down reception was completed on his side, though coaches and Porter said he did what he was supposed to on the play.

Porter has spent the better part of the past two seasons as the top backup at both cornerback positions, and played a lot this preseason and earlier in the year in place of an injured Baxter.

"You just have to be ready. It's part of being a professional," said Porter, who started the first two games. "It's one of those things ... I'm not a starter, and when my number is called, I have to be ready to play.

"My rookie year, I got some playing time quite a bit when Duane [Starks] or Chris went down. Plus that extra experience from earlier this season, that is definitely going to help me."

Porter and Baxter, along with rookie safeties Ed Reed and Will Demps, form a secondary in which none of the players started a professional game before this season.

That, though, is in line with the rest of the defense. Ray Lewis (shoulder) and Michael McCrary (knee) are also long shots to return, leaving Peter Boulware as the only defensive starter from a year ago if McAlister is out.

But even without Lewis and McCrary the past couple of weeks, the Ravens' defense (except for an early ambush by the Pittsburgh Steelers, who scored touchdowns on their first four possessions) has fared well.

Falcons quarterback Michael Vick threw for just 136 yards and rushed for minus 5. Still, it is hard to envision the cumulative effect of losing so many key components not eventually catching up with the team.

"Every team deals with injuries," defensive coordinator Mike Nolan said. "It just so happens that we are dealing with injuries to three of the four guys we've built our foundation on. Those four guys are the core of what we do and why we are doing it. But the young guys will continue to fight, play hard and try to play together as a team. They believe in what we tell them as far as playing together.

"This is certainly a challenge. When you base things around people, that means you are playing their strengths and taking away other people's strengths. Ray Lewis, McCrary and McAlister, I don't know if we will replace them right away, but we'll see."

The Bengals are usually the team ailing defenses get well against. Before Sunday, the Bengals had the 30th-ranked passing offense in the league and often, while using three quarterbacks this season, looked worse than that.

But quarterback Jon Kitna threw four touchdown passes in a 38-3 win over the expansion Houston Texans on Sunday. Peter Warrick, the Bengals' maligned receiver who was a 2000 first-round draft pick, caught one of the touchdown passes, finished with 86 receiving yards and may find an easier time against the Ravens, a team against which he has historically done little, with no McAlister.

"Obviously it would put a strain on us not having Chris out there because he is very much an impact player," Henderson said. "The way he'd been playing, I'm not sure he wasn't having a Pro Bowl season. With that in mind, what we can't do is blink and worry about not having him. Some of the other guys now have to step forward.

"There are going to be certain receivers [Porter] is going to have bad matchups with, but Chris had bad matchups, too. The one thing Porter brings is that with Gary being out early, he has shown people that he can play. He's got as much confidence in his ability now more than anything. He knows he belongs in the NFL.

"With those reps, now when he gets on the field, you won't see them going at Porter."

Next for Ravens

Opponent:Cincinnati Bengals

Site:Ravens Stadium

When:Sunday, 1 p.m.

TV/Radio:Ch. 13/WJFK (1300 AM), WQSR (102.7 FM)

Line:Ravens by 5 1/2

SunSpot:For more coverage, visit sunspot.net/ravens