World Cup winner Mustafi, who came through the ranks at Hamburg before moving to Everton in 2009, used to play as a striker.
“First of all, I'm happy now because otherwise I don't know if I would be here," he told the club's website. “But when I started, I started as a striker.
“When I was only 14, I signed for Hamburg and slowly went all the way back to the defence.
“I played in front of the defence for a few games and then in the end I ended up being a central defender and then I got a call up for the national team, for the under-15s at this time, and then it became my position."