The centre-back is keen to make the move to the Premier League before the new club season begins, but Spurs have so far been unwilling to meet the Eredivisie champions' €15 million valuation of Vertonghen.
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"Of course I'm thinking about that as there's still no clarity. We're talking about my future here. I can't say that I'm not thinking about it, and it obviously worries me," Vertonghen was quoted as saying on the official Ajax website.
"However, the fact is that there's no agreement yet, so I'll have to accept that. The most important thing for me right now is regaining match fitness.
"I'm still an Ajax player for now and will always give 100 per cent for the club. It's the start of a new season, and I'll start it at Ajax.
"It's impossible to say when this will become clearer, but it has to be well before August 31. I'm focusing on Ajax for now, though."
Vertonghen has a contract with Ajax until the summer of 2013.