KANSAS CITY, Mo. - Sean Smith's return from a suspension came at a good time for the Kansas City Chiefs.

Their top cornerback returned to the practice field Wednesday after serving his three-game suspension for violating the league's substance-abuse policy, the same day the Chiefs announced that Phillip Gaines would miss the rest of the season with a torn ACL.

Gaines had been starting along with rookie Marcus Peters while Smith was out.

"Been three long weeks," Smith said. "Can't wait to get out there with the guys."

Not only does his return coincide with Gaines's injury, it also comes with a trip to Cincinnati on Sunday. That means that Smith will likely match up with Bengals star A.J. Green, who caught 10 passes for 227 yards and two touchdowns in last weekend's 28-24 victory over Baltimore.

The two of them also matched up in 2012, when Smith was with the Dolphins.

"A.J. is a special talent, man. A rare talent," Smith said. "He's big, athletic, he can make any catch. It's definitely fun to go out there and compete with a guy like that. You have to bring you're A-game every snap because you know (Andy) Dalton is going to throw it over there."

Turns out that Green remembers the scouting report on Smith, too.

"He's a big, long cornerback, very athletic, can run, he has long arms and he likes to press," Green said. "Just take my same approach. I read every DB and try to focus on the things they do well, so I can take that away. It's same 'ol, same 'ol."

Smith was suspended for violating the NFL's substance-abuse policy after getting arrested last year for drunken driving. That is normally a two-game suspension for first-time offenders, but Smith was given an extra game for crashing into a light post.

While he was out, Smith was able to attend meetings and work out at the team's facility, but he was not able to participate in practice. That means the timing and comfort level that he established with Peters during the summer and in training camp had to be put on hold for a bit.

"I'm just glad to be back. Phil is definitely unfortunate. At the same time, I couldn't wait for these days to count down," Smith said. "I'm out here. I'm full-go."

Gaines, a former third-round draft pick, had been playing well in his first real action early this season. He was defending a pass in the end zone on Monday night when his knee twisted awkwardly and he crumpled to the turf. He was helped up soon afterward and did not return.

Gaines underwent an MRI on Tuesday that revealed the extent of the injury.

"He will have surgery on that," Chiefs coach Andy Reid confirmed after Wednesday morning's walkthrough. "We'll make the move here today to put him on IR."

The Chiefs have decent depth in the defensive backfield, though Reid refused to discuss how the pecking order would shake out beyond the starters. Jamell Flemming and Marcus Cooper figure to get more work now that Gaines is out, while rookie Steven Nelson could get into the mix.

For now, the attention is squarely on Smith and his return to the lineup.

"We've got a variety of personnel groups we can use," Reid said. "We'll go through them here and see what we can do."

NOTES: WR Albert Wilson continues to be slowed by a shoulder injury. He was supposed to be the Chiefs' No. 2 wide receiver behind Jeremy Maclin, but has just three catches for 25 yards. ... "It's a bit sore," Reid said. There was no word on whether Wilson will play Sunday.