Zverev knocked Isner out of the season-ending tournament earlier this afternoon with a 7-6(5), 6-3 victory.
The result also secured Zverev a semi-final showdown with 20-time Grand Slam winner Federer.
The pair have a close head-to-head record which Federer edges with three wins to two.
And Isner, who was on the receiving end of 18 aces today, believes the world No 5 can pull off an upset if he serves in a similar manner.
“It should be a very good match, I think one that the fans will certainly enjoy,” Isner said.
“If Sascha [Zverev] serves like that, he could have a very good shot at winning.
“We all know what Roger does so well. He serves incredibly well. It’s definitely strength on strength.”
“But I do believe, I think it will be a very close match tomorrow between those two.
a little bit.”
“You have to say Roger is the favourite. He is ranked higher right now, had a little bit better year, but only slightly.
“As I said, I think it can be a very, very close match.”
Isner made his debut at the ATP Finals this week and in doing so became the tallest player to ever compete at the event at 6ft10.
However, he was disappointed at being sent home early.
“It didn’t go as planned,” he added.
“You make this tournament, you want to do a little bit better.
“But at the same time this is no normal event. You’re up against the absolute best in the world.
“Certainly just came up short against players that were better than me this week. So I gave it my all.
“I mean, there’s definitely some things I could have done better. Didn’t come into this tournament with that much momentum. I think that maybe showed