The 27-year-old is in line to play his 17th test after being recalled to a New Zealand side desperate for top order runs against a potent South Africa pace attack.
If he plays, and the signs are he will open the batting, it will be in his first international since December 2009 but Vettori says Flynn is ripe for a return to the top flight.
"He's in off the back of three hundreds. There's no better time to come into a test match set-up when you're feeling good about yourself and you've played well," said Vettori.
The Northern Districts left-hander has chalked up 487 runs in his last five innings, including three centuries, and the runs have come at a decent clip, something he struggled to do in his first incarnation as an international cricketer.
"He's overhauled his technique and I think he's gone back to his roots in a lot of ways. He's a very aggressive player and maybe some of the public in the past might have seen him as a sort of gritty, dour, top-order batsman.
"He's turned himself into an incredibly aggressive one so he's not going to sit around and wait for things to come to him."
Flynn's first foray into test cricket was cut short when a ball from England paceman James Anderson smashed into his grill, knocking out two of his teeth and leaving a bloody mess on the Old Trafford pitch in 2008.
Surgery on a long-standing hip injury last October delayed his appearance on the domestic scene this season but he and the fit-again Dean Brownlie both appear set to feature in the test that starts on Friday.
South Africa lead the series 1-0.
