The Hammers boss is said to be interested in the Juventus striker.
Why they scouted him however is something of a mystery.
Mario Mandzukic celebrates
West Ham manager Slaven Bilic knows the striker well from his time as Croatian under-21 and senior coach.
Bilic handed him his debut for the under-21s in 2006 and against Macedonia for the senior side in March 2007.
Slaven Bilic talks tactics with Mario Mandzukic
That means the West Ham boss has known him from the age of 20 when he was still playing for NK Zagreb in his homeland capital.
West Ham need a new striker, with Andy Carroll’s continuous injury troubles and Simone Zaza and Jonathan Calleri struggling to settle in London.
Croatia's Mario Mandzukic applauds fans after the game
Mandzukic, who has also played for Atletico Madrid and Bayern Munich, is struggling for regular playing time at Juventus and would bring the sort of striking performances that the Hammers are currently lacking this season.
He has known him for ten years and Bilic would be making a wise move if he did decide to reunite with his countryman.