Since Mourinho replaced the sacked Mauricio Pochettino, Spurs have won five of his seven games in charge, which included last week's defeat at Bayern Munich in their Champions League dead rubber. Mourinho fielded a shadow XI for the game.
For his part, Sissoko has welcomed the impact made by his new manager. The France international concedes morale was low in the final days of former manager Mauricio Pochettino's reign - an issue which Mourinho immediately recognised.
Indeed, Sissoko admits it was a lack of confidence which was a major factor in the team's poor form and ultimately led to Pochettino's dismissal.
French midfielder Sissoko told RMC via Le 10 Sport: "Upon arrival, the team was mentally lifted. I think it's been him.
"When he arrived, he tried to be positive towards everyone and to restore confidence. It was the main thing to do. The qualities, we had them. Maybe there was just a lack of confidence in a lot of players."
Sissoko admits Mourinho has sought to lift the whole squad - an approach which has paid dividends with an impressive start to his appointment at Spurs.
"The psychological aspect was important," Sissoko continued.
"His arrival was good for the whole group."
- updated December 16