He acknowledged manager Antonio Conte’s impact at the north London club and said he believes they are a strong side.
Spurs appointed Conte as their manager in November after sacking Nuno Espirito Santo after a poor start to the season led them to plummet to ninth in the table.
However, under the Italian manager, Tottenham saw a turnaround in their form which enabled them to finish fourth and qualify for the Champions League.
They finished a massive 21 points behind second-placed Liverpool and 22 points behind champions Manchester City.
Spurs have made six signings so far this summer and will look to close that gap. They have signed Ivan Perisic, Fraser Forster, Yves Bissouma, Richarlison, Clement Lenglet and Djed Spence.
Henderson believes these signings and Conte’s management could help the north London side challenge the top two. He told talkSPORT:
“At the start of every season you look at other teams around improving, bringing new players in, new managers in. You might get a team you think might not be in the top three, top four, top five but actually have a really good season and are in there. So anything can happen.”
“If I look at Spurs, who qualified for the Champions League, Antonio Conte has done a good job since he’s gone in and has brought some really good players in. They’ll be stronger again.”
Tottenham started their Premier League campaign on a winning note, beating Southampton 4-1 at home. Liverpool, meanwhile, played out a surprising 2-2 draw away against newly-promoted Fulham.