That’s according to Greg Rusedski.
Federer faces Isner in the championship match in south Florida today (6pm UK time) with a three-time Miami winner, in the Swiss icon, taking on the reigning champion.
The 37-year-old has been in sumptuous form of late, with this his third successive final on the ATP Tour after winning in Dubai and losing to Dominic Thiem in Indian Wells earlier this month.
But Federer faces a unique challenge against Isner in what will be their first meeting on tour in four years, though they played each other in last year’s Laver Cup.
Isner is the tallest guy on tour and has a booming serve to match, which when used at its best leaves his opponents with very little chance of returning the ball.
The big-hitting American is 11 matches without defeat in this Masters 1000 tournament having secured the crown in Key Biscayne, the event’s previous base 20 miles away from the new headquarters of the Hard Rock Stadium.
And so far this year, Isner is a perfect nine wins from nine in the tiebreakers he has played – with nine of the 10 sets he has played in Miami Gardens having been decided by one.
While Federer has the weaponry to overcome Isner’s advantages, former world No 4 and Miami Open analyst Rusedski insists Isner’s staff should be telling him to make the most of his dreaded serve.
He told Amazon Prime: “I look at Roger Federer, he’s got that beautiful block return of serve.
“That makes a huge difference against a big server.
“He always finds a way to get it back in the big moments.
“What I’m looking for, what I want to see is Federer play some tiebreakers.
“There’s been a few question marks, once in a while, how he’s handling those break points and those big situations.
“If I’m Isner’s coach I’m saying, ‘Focus on your serve, take risks on the return and anything can happen.’
“I’m hoping to see some tiebreakers in that final and I’m sure John knows that as well.”
Federer owns a 5-2 career record against Isner but knows full well the task ahead of him.
He explained when asked how he will look to conquer Isner’s serve: “It’s a tricky one. Sometimes you go with momentum, sometimes with feel, sometimes you guess a little bit and sometimes you actually see it.
“It’s a combination of things. Some days you feel it better than others.
“Let’s say I know he’s going to be T, let’s say he told me that before the serve, that still doesn’t mean I’m going to hit a return winner because the margins are slim when it comes in so fast and so high.
“First, you want to connect. Secondly you want to get in a neutral position, which is very difficult, because you know he’s looking for his forehand or he looks to come in or try to take charge of the point.
“It’s tough, you just hope the stars align and that you pick the right side, he picks the wrong side, maybe he misses a serve and you try to put him in uncomfortable situations time and again, and at the end of it you somehow find a way.
“But he has a serve you basically cannot read. It’s that simple.”