"Danica, I think she's got the talent and everything, but I don't think she knows what she's getting into," he told reporters Friday before rain washed out qualifying at New Hampshire Motor Speedway.
Montoya can speak to this better than most. The former Indianapolis 500 champion left Formula One three years ago to pursue a career in the Sprint Cup Series.
He's won on a road course, which came as no surprise since he is one of the best road course drivers in the country. He hasn't won on an oval and hasn't qualified for the Chase, although he is 12th with 10 races remaining before the 12-driver playoff field is set.
"They're so different to drive," said Montoya, explaining the difference between a stock car and Indy car. "It's not the same feeling. When you drive an open-wheel car on an oval you have the grip, you turn the wheel and it turns, you get on it and it goes and you get on the brakes and it stops.
"This it goes more with the momentum," he said of stock cars. "You've got to give time to the car and you've got to get used to the feeling that you've got to go fast when the car doesn't feel right. With time actually it becomes kind of normal."
But again, it takes time.
And Patrick's credentials aren't nearly what Montoya's were when he made the jump. He is the only driver to win the open wheel CART title, the Indianapolis 500 and 24 Hours of Daytona -- all on his first attempt.
He won numerous other races and titles in open wheel.
In Cup he finished 20th in points as a rookie and 25th in 2008. He has only one win and five top-5s in 89 races and has led only 51 laps.
Patrick has finished no better than fifth in points since joining the IndyCar Series in 2005, and she has only one win in 71 races.
But her contract with Andretti Green is over after this season and she insists she's looking at NASCAR, although many such as myself believe she's using the sport for leverage to get more money out of the IRL.
There has been speculation that she will join Chip Ganassi, the co-owner of Montoya's Cup team, in the IRL.
If she passes on that or other IRL offers for Cup, where she's made it clear she'd want to be with a top organization right away, it likely will take a few years in the Nationwide Series as well as the Cup series to help her adjust to stock cars.
If she makes the move, there's no guarantee she'll succeed even though sponsors would line up for the opportunity to partner with her. Dario Franchitti was gone from Cup within a year due to lack of sponsorship at Ganassi Racing. Sam Hornish Jr. is 26th in points for Penske Racing after a couple of years in NASCAR's premier series.
Both won Indianapolis 500s.
Patrick has not.
The NASCAR path, if she chooses it, will not be easy.
"If she comes, I'm sure she can do it, but it doesn't matter if you come to a winning team or anything," Montoya said. "It's going to take time."