Ronaldo was booked for diving during the Carling Cup final win over Spurs on Sunday following a challenge by Tottenham skipper Ledley King in the 18-yard box.
Although the 24-year-old winger insists he did not cheat at Wembley, the former Sporting Lisbon man has earned himself an unwanted reputation during his time at United.
The Fifa World Player of the Year has never endeared himself to the English public after famously winking when Wayne Rooney was sent off for England against Portugal in the quarter-finals of the 2006 World Cup.
And Modric struggles to understand why a player of Ronaldo's calibre resorts to such exaggerations when he is on the field.
"He's an excellent player, but he really overdoes the theatrical bits," Modric told Sportske Novosti.
"In England, where fairness is especially kept in mind and where a masculine, fair game is the law, such whining stands out even more.
"I don't know what good it will do him."