The Gunners are now just seven points behind fifth-placed West Ham, and are in a good position in the Europa League.
Mikel Arteta will see his side face Olympiacos on Thursday night with a 3-1 lead from the first leg and one foot in the quarter finals.
But Leno believes there was a “bad atmosphere” earlier in the season after a poor run of form.
However, Leno believes the team has now turned the corner and are confident ahead of the closing stages of the campaign.
“We were completely lacking the consistency,” the Gunners goalkeeper said.
“In [the] autumn, we had big problems, a bad atmosphere… and we turned the corner.
“Qualifying for] Champions League will be very, very difficult.”
Leno went on to discuss the importance of Sunday’s win over Spurs, and discussed the potential of making a challenge for the top four.
Arsenal are still tenth in the Premier League table, but are level on points with Aston Villa, the team above them.
Leno continued: “Hopefully it will increase the level of confidence of the team and the belief that we can play really well against any opponent.
“We can beat big teams as well and just maintain everybody together with a big belief.
“We know we have to put four or five wins together in a row to give ourselves any chance of looking up in the table, but we are ready for a fight.”