Di Maria, 26, joined United in August for a British record transfer fee of £59.7 million and has made a bright start to life in the Premier League.
The attacker has three league goals already this season, including one - and an assist - in United's 2-1 win over Everton on Sunday.
Heinze, who was at United from 2004-07, said Di Maria deserved to be considered alongside the likes of Cristiano Ronaldo and Lionel Messi and among the world's best.
"Anything I can say about Angel Di Maria is not enough," Heinze said.
"For me he is one the four best players of the world, he's at an amazing level and has now arrived at an amazing club, where they will look after him very well and he will perform very well."
Heinze said Di Maria would have no problems settling in England and believes United will play a key role in helping him adapt.
"I don't know if it is a problem for Di Maria to play in a new country," he said.
"I think everything takes time, especially for the English league, you need to adapt, but the club will help you.
"Manchester United make things easier for you."
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