Mauricio Pochettino expects Tottenham to respond from the loss to Leicester when Sunderland visit White Hart Lane on Saturday.
Spurs conceded a late Robert Huth goal to fall seven points behind the Foxes and Arsenal in fourth place in the Premier League.
Pochettino, who again reiterated striker Harry Kane is not for sale, said: "We missed a great opportunity to establish us on the top and you feel disappointed but you need to carry on and keep working hard.
"It's a very open league. So far anything can happen. All (clubs) in the top 10 have the possibility to win the league.
"We played well, we deserved more, but in football you need sometimes to have some luck. It wasn't for us last night.
"In the way we played last night it's nothing to worry (about) for the future.
"We have a quick game on Saturday. It's very important. We must react, play well and take the three points, because we need to keep our position in the table."
Spurs spurned opportunities and Pochettino remains in search of a striker to ease the burden on Kane.
Kane was recently linked with a move to Real Madrid, who on Thursday, along with city rivals Atletico, were hit by a FIFA ban on incoming players in the next two complete transfer windows.
Real, banned over transfers involving under-18s, can sign players this month, but Kane will not be among them.
"Harry Kane is not for sale," added Pochettino, who is looking for a player to complement the talents of his talisman.
"We cannot change after one result our plan and our view about our squad.
"I've explained a lot of times that if we find the right profile and the player that can improve our squad, we work hard for that.
"If we can add some player, we are open (to it)."
Pochettino would not be drawn on whether he is looking for someone to play alongside Kane or to slot in for the striker to grant a rest.
"The profile is a different profile than we have, that can help us, that sometimes can help with Harry and improve our squad," the Argentine added.
Pochettino also declined to comment on reports midfielder Mousa Dembele is discussing terms over a new contract.
"This is a private issue. I never speak in public about a private matter," he said.
Tottenham are likely to have an unchanged squad for Saturday's match, with Ryan Mason missing the Leicester contest with an ankle problem.