Javier Hernandez has questioned David Moyes and Louis van Gaal 's handling of his game-time during his last two years at Manchester United .
'Chicharito', brought to Manchester by Alex Ferguson for a knockdown £6m in 2010, is in prolific form at Bayer Leverkusen as his former teammates toil under Van Gaal's questionable management.
The Mexican started just 12 games under Moyes in 2013-14 and was handed only two starts and two substitute appearances by Van Gaal.
Hernandez, who scored a 13-minute hat-trick against Borussia Monchengladbach at the weekend, remains fond of Ferguson and feels his successors could have learnt from his squad rotation prowess.
"My time at Manchester United was good," Hernandez said. "I had an incredible start with many opportunities, but ended badly because of a lack of opportunities, but I am totally grateful towards Ferguson.
"I think he is the best manager in history, in the way he managed his players. He gave everyone a chance and understood that a player cannot finish a season with only 15 games. He opened the doors to Europe for me and I also won two league titles under him."
Hernandez was voted the Sir Matt Busby Player of the Year after his first United season by supporters and his knack for vital goals endeared him to Reds during his five years at the club.
In three seasons, Hernandez netted 23 winners in all competitions.
Since joining Leverkusen, Hernandez has scored 13 goals in all competitions and could face United again in the latter stages of the Europa League.