The midfielder has agreed to move to White Hart Lane at the end of the season, when his contract expires, but the north London club are looking to bring him in earlier after Sandro was ruled out for the rest of the season with a knee injury.
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Goal.com revealed on Thursday that Andre Villas-Boas' side had reacted to the Brazilian's injury by approaching the Bundesliga side about an earlier move for Holtby than originaly scheduled.
“We are in talks about a move in this transfer period, but there is no agreement,” Heldt told Sky Sport before Schalke’s game with Hannover on Friday night.
“Tottenham contacted us, because they want Lewis now. We will decide in the coming days.”
Heldt also dismissed claims that Holtby could try and engineer a move away from the Veltins Arena, and says that he will continue playing for the team regardless of speculation.
He added: "Lewis is a good character, he will give everything to the last day for the club."