Zverev, who is contesting the tournament for the first time, won his opening match against Marin Cilic on Sunday and can also progress to the last four provided he beats the eighth seed Jack Sock in their final match of the Boris Becker group on Thursday.
“I like what I see with Alex,” said Federer. “I see somebody who is working towards the future and yes, it’s important to have success right now, and he’s had that with two massive titles at the Rome and Montreal Masters. But what I like to see is that he is working towards how he could be playing when he is 23 or 24 in terms of fitness and planning and organisation.”
Federer was one of the casualties of the German’s success. The Swiss lost to him on the hard courts in Montreal in August. Former world number one Novak Djokovic was blitzed on the clay in Rome. Three other titles have been collected by the youngster.
“What I like is that Alex has got the full package,” added Federer. “He is already number three in the world and whether he makes the semi-finals or not in London, he is going to leave the ATP Finals with a lot of information because the last six months of the season have given him everything he needs to work on and he’s only going to get stronger from here so that’s encouraging for him and his team.”
For Zverev, composure will be high on the list of attributes to master. After saving two set points, he took the first set into a tiebreak and led 4-0. But he let Federer claw his way back in and squandered his own set point before losing the shootout 8-6.
He capitalised on wayward shots from Federer to win the second 7-5 but seemingly ran out of steam in the decider losing five consecutive games to slump 6-1.
“In the final set, he played a very good game to break me,” Zverev said. “And after that I lost a little bit of concentration. But overall I think it was a positive match for me.
"I played better against Roger than I did in my first match against Marin and I still think I have a very good chance to qualify. And if I play at the level I showed against Roger, maybe I’ll be here at the end of the tournament.”