Former Real Madrid and Barcelona midfielder Robert Prosinecki says he was shocked to see Gonzalo Higuain make his Juventus debut looking "even more fat than me".

The Argentina international, who scored 38 times in 42 appearances for Napoli last season, joined the Serie A champions for a club record fee of €90million last month.

The 28-year-old looked overweight when he played his first game for the club in last week's friendly win over West Ham, prompting criticism from some fans on social media, as well as Napoli president Aurelio De Laurentiis.

Prosinecki admitted he was amazed by his fellow former Madrid man's questionable physique, but has backed Massimiliano Allegri to get him fit and firing in time for the season opener against Fiorentina on August 20.

"I was shocked to see Higuain, he is even more fat than me!" he told Jutarnji List. "They paid 94 million [sic] for him and he's arrived as a 'little pig'!

"I can imagine how shocked Allegri was, after he insisted on his signing. But they will make him fit soon."

Former Croatia star Prosinecki, who has been head coach of Azerbaijan since 2014, has also backed Zlatan Ibrahimovic to make a huge impact following his move to Manchester United.

The 34-year-old proclaimed he will become "God in Manchester" after signing a two-year deal at Old Trafford, and Prosinecki has no doubt he will prove prolific and fulfil his typically grandiose prophecy in the Premier League.

"I was amazed by Ibrahimovic, he didn't even seem so good at PSG," he said. "He will score 30 in England and become God in Manchester."