''Trumaine is up and ready to roll,'' defensive coordinator Greg Williams said after practice Friday. ''I'm anxious to watch him play again. He's been playing well all year. He'll be fine.''
St. Louis has just four cornerbacks on the roster. With Johnson out and Jenkins getting hurt, the Rams finished Sunday's 27-3 loss to Arizona with only Marcus Roberson and Lamarcus Joyner at the spot.
Jenkins twice had collisions with teammates against the Cardinals. Early in the game, Jenkins and McDonald ran into each other on a pass from Carson Palmer to Michael Floyd. Jenkins was then checked for concussion symptoms.
Jenkins left the game and did not come back.
In his fourth season, Jenkins had his team high 12th pass breakup before leaving the Arizona game with a concussion. He has three interceptions and 52 tackles in 12 games.
Jenkins did not practice this week.
''He's in the (concussion) protocol and is listed as doubtful,'' coach Jeff Fisher said.
Getting Johnson back will help soften the blow of missing Jenkins.
Johnson got his team-leading fourth interception when he picked off Baltimore's Joe Flacco and returned it 25 yards in the third quarter in Week 11. He pulled his thigh on the play and has not played since.
''I knew the second it happened,'' Johnson said. ''I couldn't run no more. It would have been six, for sure. But now I'm back. It's not going to be 100 (percent) but it's good enough to play on Sunday.''
Johnson is looking forward to being matched against Detroit receiver Calvin Johnson.
''He's a beast, one of the best. He's big and physical,'' he said. ''He's a good receiver. I'm looking forward to it. It's going to be fun, a Johnson versus Johnson show on Sunday.''
''Yeah, we've got our work cut out for us but there opportunity there, too,'' Williams said. ''Can we make some breaks on the ball? Can we do a good job on pass breakups? Can we rush the passer? Coverage and rush all go hand in hand.''
The Rams remain without two-time Pro Bowl end Robert Quinn, who will undergo back surgery. Quinn started the first seven games.
After missing a game, Quinn played sparingly against Chicago. He has been inactive for the last three games.
Eugene Sims has stepped into Quinn's spot.
''Eugene has done well,'' Williams said. ''He's gotten better and better. Eugene may be the toughest individual in that entire building. If a fight broke out, I'd want to go stand behind him. That's not a lot of fall-off from just the toughness aspect of it.''
''Robert is a rare pass rusher. There's not many people that can do the things he can do in this league. He's blessed.''
McDonald will have shoulder surgery. He is a valued member of the secondary where he is a weapon in run support. He also ranks among the hardest hitters which makes receivers wary.
Backup Maurice Alexander, a core special teams player, will start in McDonald's spot. It will be the second start for the second-year pro, his first coming Nov. 8 at Minnesota. He has two sacks this season.
''He's come a long way. He had a great preseason,'' Fisher said. ''When he's played, with the exception of one touchdown pass that caught him with his eyes in the wrong place, but when he filled in for T.J., he did a nice job. We're expecting him to finish up the year strong. It'll be a really good opportunity for him.''
''I'm excited, man. I'm ready to go,'' Alexander said. ''There's a good group of receivers over there in Detroit and it'll be a challenge.''
NOTES: The Rams will wear special all yellow uniforms for next Thursday night's home game, the final one in 2015, against Tampa Bay. In practice Friday, numerous players wore the all yellow cleats. ... TE Lance Kendricks is listed as probable and has passed the NFL concussion protocol. ... Also listed as probable are WR West Welker (calf), QB Case Keenum (concussion), DE William Hayes (thigh), and K Zach Hocker (thigh).