Barca doctor Ricard Pruna said earlier this summer that the 21-year-old must gain weight in order to reach his peak physical condition, after the Brazilian was diagnosed with anaemia following his €57 million [£48m] switch to Camp Nou.
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"If Neymar puts on weight, they’re going to take away everything that’s best about him," Ramalho told Jovem Pam.
"They’re going to take away his speed. With small players such as Xavi, [Andres] Iniesta and [Lionel] Messi at Barca, I never imagined that they would do this.
"If he puts on weight he could suffer a knee injury, like what happened to Ronaldo. It’s a dangerous business."
Neymar scored his first goal for Barcelona earlier this week in the 7-1 friendly win over Thailand.