The Bavarians have been in fine form all season and are on the brink of securing a top-eight finish in the Champions League first phase with two matches remaining. They are in second place on 15 points, with the top eight teams advancing automatically to the round of 16.
They are undefeated in the Bundesliga and are 11 points clear at the top of the table following their impressive 5-1 comeback win at RB Leipzig on Saturday, and also saw fit-again playmaker Jamal Musiala make a comeback in that game after six months out with a broken leg and ankle.
With a 16-3 goal difference in their three matches so far this year, Bayern are firing on all cylinders but for Kompany, Wednesday's game will not be a walk in the park.
"I was probably the first who said in a press conference (as Anderlecht coach between 2020-22) that they are doing very good work," Kompany told a press conference. "I said 'this is not an easy opponent, they will play for titles very soon.'
"What I mean is they work super hard, have talented players, and it is a club that knows their underdog role for years, and uses that well. I have a lot of respect for them."
Union are in top spot in the Belgian league but are battling for a top-24 finish in Europe that would ensure they go into a playoff for a spot in the knockout stage. They are currently 27th on six points.
But for Kompany, whose team have won five of their six Champions League matches this season, they are still a dangerous side away from home.
"They are underdogs, they are compact and they can have these hero moments," Kompany said. "No club has done it better in Belgium in the past five years."
