Monteiro made his league debut for Servette at the age of 16, becoming the third youngest player to make an appearance in the Swiss Super League.
He has played seven times in all competitions for the Maroons, who currently sit third in the league table.
The defender has also made a number of international appearances through various age groups for Portugal, from Under-15 to Under-19 levels, representing the country over 30 times.
The recently turned 18-year-old has agreed a three-and-a-half year contract at Elland Road and will initially join up with Michael Skubala’s Under-21s squad, as they continue to battle for promotion from Premier League 2 Division 2.