The former striker says their lack of depth could be a big problem as they aim to reach the Champions League.
They are unbeaten since their opening-day loss to Manchester United, having put in a series of impressive performances over the first 11 games of the season.
Mauricio Pochettino and his side will be hopeful their strong start can help them finish in the top four come the end of the campaign but Nicholas says a lack of depth could end up costing them dearly.
"Tottenham have got a real shot at finishing in the top four but, when I watched them take the lead at the Emirates, they had the chance to kick on and win that match but weren't adventurous enough," he told Sky Sports.
"There are also still issues with depth. Their centre-backs have done really well but where's the cover? I'm not a fan of their full-backs and they rely on Harry Kane and Hugo Lloris a lot."
Given how well they have performed so far this term, there is a huge chance Spurs could be challengers for the top four this season.
Nicholas's point about depth, however, is a good one, with Tottenham being heavily reliant on certain stars in some areas.
January provides a good opportunity to provide cover for Harr Kane in the centre-forward area, while - as Nicholas says - the back four is an area for concern in terms of depth, even though Tottenham's first-choice back four are in supreme form.