Right-back: Aaron Wan-Bissaka (Manchester United)
His attacking output leaves a lot to be desired but Wan-Bissaka more than makes up for that with his defensive prowess.
He's been criticized lately for rusty performances but the Englishman responded with a talismanic display against Tottenham Hotspur at the weekend. He even produced a superb block on Heung-min Son, who had run past United's backline and was almost one-on-one with the keeper.
Centre-back: Raphael Varane (Manchester United)
Varane's importance to Manchester United was clear when he returned from injury at the weekend. The side ended up registering their first clean sheet in 10 games!
In fact, they've conceded only six times in the seven games that he's played, as compared to 14 on the other six occasions that he didn't.
An accomplished centre-back with an envious trophy cabinet to boast, the Frenchman will be valuable in shutting out Atalanta tomorrow.
Centre-back: Marten De Roon (Atalanta)
From playing in the Championship with Middlesbrough in 2017 to starring for Atalanta, De Roon has certainly come a long way in the last few years.
A defensive midfielder by trade, his versatility has allowed the Dutchman to excel in a centre-back position too. He is known for reading the game brilliantly and timing his tackles to perfection.
He has averaged close to three tackles per game in the competition this season and has made eight ball recoveries. His stoppage-time equalizer against Lazio at the weekend showed he's got an eye for goal too.
Left-back: Luke Shaw (Manchester United)
Shaw is another player who recovered from a horrow show against Liverpool with a solid performance last weekend. He will look to continue in the same vein on Wednesday.
The 26-year-old is an excellent passer of the ball. He has been dominant aerially too, averaging three duels won per game in the Champions League this season.
He also assisted Ronaldo for United's winning goal against Atalanta last month with a sensational cross. More heroics to follow?