This was the third award this season for Ranieri, who was named Italian football's coach of the season on Monday for his extraordinary achievement in guiding Leicester to the most unlikely of Premier League triumphs.
Aguero scored in all of City's five games in April, including a stunning hat-trick in the win against Chelsea at Stamford Bridge on April 16.
The Argentine has struggled with injuries this term but still managed 23 league goals, and is in contention with Harry Kane (25 goals) and Jamie Vardy (24) for the golden boot, despite playing 900 minutes less than the pair.
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Aguero's goals have put his club in the driving seat in the race to finish in the top four, as City need a draw in Sunday's trip to Swansea City to confirm their qualification for next season's Champions League.
(Reporting by Shravanth Vijayakumar in Bengaluru)
