Valtteri Bottas is a "more complete" driver than 2016 world champion Nico Rosberg.
"Valtteri Bottas is a more complete driver than Nico Rosberg," the Colombian is quoted by AS newspaper.
"Last year was very hard for him, but he has been able to recover and what he is doing now is very good."
Where Rosberg and Bottas are similar, Montoya agrees, is the way they are often able to rattle the five time world champion Hamilton.
"You see Lewis start to make mistakes in practice that he usually doesn't make," said Montoya. "When you start to make mistakes to go fast, it means you're finding it more difficult."