Zverev famously came out against this new format, which, to him, completely went away from what the Davis Cup is supposed to be. He even famously said that he wouldn't play in it until the format returned to the usual one but has gone back on the promise by opting to play for Germany since then.
He played in the qualifiers last year and did fine, but he won't be playing this year, even though Germany needs him. The country is playing against Hungary on the outskirts of Budapest, and it's a competitive matchup.
The German team without Zverev is certainly favored to win the tie, but it's far from an easy one. It would be far easier with Zverev who has been playing really well so far this year. He's 9-2, including a sensational performance at the United Cup, where he led Germany to a trophy.
Unfortunately for the country, Zverev hasn't recovered from an illness that plagued him in the final stages of the Australian Open. He talked a little about that after losing to Daniil Medvedev, admitting to an illness, but wouldn't go into too much detail.
He's yet to fully recover from it, and it will keep him away from the qualifiers. We'll see what happens next and whether Zverev returns during the brief indoor European season. Maybe he'll play in Rotterdam, but if not, then likely in the Middle East.
In Zverev's absence, the country will rely upon Dominik Koepfer and Jan-Lennard Struff. They're certainly capable of getting the win for the country, but it's going to be complicated. The doubles might prove crucial, with Tim Puetz and Kevin Krawietz looking to finish it.