(Reuters) - Tottenham Hotspur manager Mauricio Pochettino has praised Son Heung-min for stepping up in Harry Kane's absence, adding that the forward "is on fire" after scoring the winner in Tuesday's 1-0 Champions League victory at CSKA Moscow.

Kane was the club's top scorer in the last two seasons and has netted twice in five league appearances this campaign but the England striker sustained an ankle injury earlier this month.

Meanwhile, South Korea international Son has scored five goals in all competitions for Spurs this season, including a brace in Saturday's 2-1 Premier League win at Middlesbrough.

"I think it is key. It is very important that not only Harry, who was good before his injury and scored, that now another player has scored and that is very important for the team," Pochettino told reporters.

"I feel very pleased for Sonny. He is on fire and to keep this form is very important for us."

Pochettino also explained the reasoning behind his decision to replace striker Vincent Janssen, top scorer in the Dutch league last season, with winger Georges-Kevin N'Koudou a few minutes before Son scored the winning goal in Moscow.

"We tried to find more mobility in our offensive position. It is for that reason we changed Vincent for N'Koudou, to have more pace down the sides," he added.

"First touch we find the link and it was fantastic the goal. Sometimes when you change, it goes well and sometimes no."

(Reporting by Ian Rodricks in Bengaluru; Editing by John O'Brien)