Former Tottenham midfielder Sandro has told ESPN Brasil that Harry Kane's teammates used to make fun of him but says the striker now deserves his place among the elite.
Sandro spent four years at Spurs before joining Queens' Park Rangers in September 2014, at the start of Kane's breakthrough season under Mauricio Pochettino.
He recalled Kane's hunger to improve as a young player and says they used to be in direct competition in training.
"Kane, I define in one word: 'Worker,'" Sandro, currently on loan at Serie A club Benevento, said.
"All he does is a matter of training and confidence. Since when he was young me and [former Spurs goalkeeper Heurelho] Gomes spoke of him: 'Damn, the kid is impossible, is training very well.'
"He used to call me to mark him in training because he knew I gave everything in all the works. 'Come, Sandro, mark me I will come up against you!
"Sometimes the other players would look at each other and make a banter, 'Look Harry Kane... Poor guy, he thinks he's going to play.' It was as if they wanted to say: 'I'm going to play' and he stays there just training."
Kane made his Spurs debut under Harry Redknapp in a UEFA Cup match against Hearts in August 2011 and his Premier League bow followed a year later as an 85th-minute replacement for Sandro in a 2-1 defeat at Newcastle.
"Sky Sports did this story the other day and I did not even remember it," Sandro said. "So I can say I'm marked in his story too.
"I'm very happy for everything that happened to him, because he's a very humble and hard-working guy, he deserves to be at that level, because the status he reached was not something overnight. He came evolving each season and now he's on top of the world."
After spending the remainder of the 2012-13 season on loan at Norwich and Leicester, Kane joined the first team the following year and began to earn minutes under Andre Villas-Boas and then Tim Sherwood.
Sandro remembers how the young striker, then still a teenager, began to grow in stature and says he felt it was only a matter of time before he "exploded" into the first team -- as he eventually did under Pochettino.
"There was a year he had a little more time with us, training with Andre Villas-Boas. He was in the squad and he started to gain weight with the team, because he's very polite and everyone loved him," Sandro said.
"But he was seen only as 'an academy boy', so they did not give him much weight. Today I even understand, because to play for Tottenham you have to be 'flying.' He was new, so they thought he needed to pick up experience in other places, so he would come and go.
"But then he started doing some cup games, like the Europa League, FA Cup, and he scored a few goals here and there, and I thought: 'Cool, look at Kane scoring a goal.' He started to get more and more strength inside the group, and it was clear that the time was coming for him to explode."