This will be the first of the two-legged fixtures between the sides, who have last squared off in 2019.
The hosts have kicked off the MLS 2021 season on a positive note. They played out a goalless draw in their season opener but recorded a superb 3-1 win over Chicago Fire in their previous outing.
The Union were impressive in their last 16 win over Deportivo Saprissa but have scored just once in two league games. They also played out a goalless draw in their first game of the 2021 season but fell 2-1 to Inter Miami at home on Saturday.
Atlanta United vs Philadelphia Union Head-to-Head
The two clubs have squared off seven times so far. Six meetings have come in the MLS regular season while one was in the playoffs. They have never crossed paths in the CONCACAF Champions League.
This is the debut season in the continental competition for the Doops. Meanwhile, The Five Stripes have made it to this stage of the tournament for three consecutive seasons.
The hosts have a superior record against their Eastern Conference foes and have four wins to their name. Philadelphia have just one win while two games have ended in draws.
They last met in the MLS Playoffs in 2019. Atlanta United cruised to a 2-0 win in that fixture.
Atlanta United form guide across all competitions: W-D-W-W
Philadelphia Union form guide across all competitions: L-D-W-W
Atlanta United vs Philadelphia Union Team News
Goalkeeper Alec Kann and midfielder Mo Adams are the two injury concerns for the hosts in this first-leg tie. Kann has a shoulder injury while Adams is expected to be out for another month on account of a hernia injury.
Meanwhile, first-choice goalkeeper Brad Guzan will be able to return between the sticks in this game. He picked up a red card in the first leg of the round of 16 fixtures and was suspended for their last Champions League game.
Matheus Rossetto has obtained a US green card and can mark his return to the squad, as he will no longer occupy the club's international spot.
Injured: Mo Adams, Alec Kann
The only injury concern for Union at the moment is veteran midfielder Ilsinho, who injured himself in the loss against Inter Miami just 11 minutes after coming off the bench.
Jack de Vries is recovering from a concussion and might not make the trip.
Injured: Jack de Vries, Ilsinho
Atlanta United vs Philadelphia Union Predicted XI
Atlanta United Predicted XI (4-3-3): Brad Guzan; Alan Franco, Anton Walkes, Miles Robinson, George Bello; Santiago Sosa, Emerson Hyndman, Ezequiel Barco; Marcelino Moreno, Jake Mulraney; Lisandro López
Philadelphia Union Predicted XI (4-3-1-2): Andre Blake; Jack Elliot, Jakob Glesnes, Oliver Mbaizo, Kai Wagner; José Martínez, Leon Flach, Alejandro Bedoya; Jamiro Monteiro; Kacper Przybylko, Sergio Santos
Atlanta United vs Philadelphia Union Prediction
Philadelphia Union have seen a sudden drop in form in the MLS after scoring five goals in the CONCACAF Champions League round of 16 fixtures.
Atlanta are unbeaten in all competitive fixtures this season. Given their form at the moment, we do not expect them to drop points at home. A win for the home team looks like the most likely outcome.
Prediction: Atlanta United 1-0 Philadelphia