The north London outfit beat off interest from domestic rivals Arsenal and Liverpool to seal a deal which will see the 22-year-old move to White Hart Lane when his current contract at Schalke expires in the summer.
But Eberl, who takes charge of player development at Holtby's former club, has doubts over the Germany international's ability to cope with the increased physicality of life in the Premier League.
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"Lewis Holtby is from our youth academy,” said Eberl. “We educated him since [he was] 15 years old then he went to Alemannia Aachen and the rest of the career is known. And now he decided to go to Tottenham.
“I think it's a big step for him. I hope he will play for Tottenham because it's a very good team. The Premier League, it's a very competitive league.
“So he decided to go this way and everybody will wait and see what happens. But he has technical quality, he has the football quality. But I think he needs physical quality too, in England, in the Premier League, and that will be the little question mark [over his ability]."
Holtby has made 17 appearances in the Bundesliga for his current side so far this season - scoring three times and making five assists.