Boris Becker was not shocked to see Alexander Zverev lose to Michael Mmoh as he didn't play an official tournament in seven months before the Australian Open.
Zverev played some exhibition matches and did okay albeit the struggles were clearly visible. It showed up in Australia there as Zverev was unable to handle Mmoh who was simply better and won. His problem was not being able to keep up with Mmoh physically as he clearly lacks matches. Becker pointed that out in his analysis as well:
"I wasn't totally surprised that Sascha Zverev struggled in his second round. We should not forget. He didn't really play an official tournament in 7 months. The first round was really difficult. He won in five sets and physically it's tough for him to be in any kind of shape at all."
Zverev really struggled physically and it became worse as the match went on. He admitted himself that he'll need time to get back into the shape he had at the time of his injury. Becker also added:
"I thought he would struggle physically and that's what he did. I think he tried hard, he gave everything he had in the tank but I don't think the tank is really full."