Milan have confirmed on their official website that the gifted attacker has joined first-team training this week at the tender age of 15 years, 10 month and 28 days old.
The Rossoneri take on Sassuolo at the weekend in their last match of the 2013-14 campaign and Milan suggest on their website that there is a realistic chance Mastour will make the squad for Sunday's game at San Siro.
The Italy Under-16 international joined Milan from Reggiana in the summer of 2012 and is regarded as one of the biggest talents around in the game worldwide.
Paolo Maldini currently holds the record for youngest first-team player, having made his debut aged 16 years and 208 days against Udinese on January 20, 1985.
Other youngsters to have made their first-team debut in recent years include Bryan Cristante (16 years and 9 months) and Mattia De Sciglio (18 years and 11 months).
