Spurs appeared last week to be close to completing a £60m deal for the midfielder, but it had since emerged that Nottingham Forest are said to be considering legal action.
The 25-year-old has trained this week with Forest and it remains to be seen whether Spurs press ahead with the move, but Frank gave little away when asked about the situation.
"You know me well, so I'll use what I've done all the time," Frank said.
"I'll not speak about players that are not mine. I think I've done two exceptions and they're getting older, that's [Cristiano] Ronaldo and [Lionel] Messi. The rest I'll just speak about the players that are inside the squad of Tottenham."
Frank described the 24-year-old as being at "the perfect age" and praised the club's hierarchy for getting the deal done before the start of pre-season.
"Top work from Daniel [Levy], Vinai [Venkatesham] and Johan [Lange] in getting a very good player in early in the pre-season so we can start working with him.
"I think he gives us a bit of that unpredictability in the game. I think he's one-on-one actions are top, I think he's slide passes are top, I think his finishing is very good. He is almost the perfect age to perform but also to take the next level."