Tottenham forward Son Heung-min believes Olympic heartache has played a major part in his superb start to the season.

Son scored the winner in a hard-fought 1-0 win over CSKA Moscow in the Champions League on Tuesday night to lift Spurs up to second in Group E, and only one point behind leaders AS Monaco.

The goal extends Son's excellent streak, which has seen him notch five in five games in the current campaign and three in his last two following his brace against Middlesbrough on Saturday.

It also extends a remarkable turn of fortunes for the 24-year-old, who came close to leaving Tottenham last summer, only to be persuaded by manager Mauricio Pochettino to stay and fight for his place.

Son had been unhappy with starting only 13 Premier League matches last season and there was also friction over his decision to represent South Korea at the Olympics, which meant he missed pre-season and Spurs' first three matches this term.

The former Bayer Leverkusen frontman, however, insists reaching the quarter-finals in Rio, and losing there to Honduras, has contributed greatly to his recent form.

"After the Olympics I was very upset," Son said.

"I was really down because I play for my country and want to get some medals for my country. For six months I was preparing but after Olympics I thought now I have to focus on the season.

"It was not easy but everyone, my family, my team-mates, help me a lot and that made me stronger than before.

"I had pre-season and I feel really fit. We played maybe four games at the Olympics so I feel very fit.

"It is true I am in great form and have made a great start but I have to keep working hard so I finish like this."

Son's sharpness in front of goal has also been timely given the absence of Harry Kane, who remains out with an ankle ligament injury and is set for at least another month on the sidelines.

Pochettino substituted Vincent Janssen in the second half in Moscow before pushing Son up front, and the Argentinian now has a decision to make ahead of Sunday's crunch match against Manchester City.

The Spurs boss admitted after their win over CSKA that Son was "on fire" and it could be he is preferred to Janssen in the central striker's berth this weekend.

"I am very happy to hear these words 'on fire'" Son said.

"I don't know what to say, I try my best and I want to help my team-mates every game. The team-mates help me a lot.

"I try, I can't say I score for sure but I try as an offensive player to score and score the winning goals.

"But I think we have great players to score. Harry is a great player but also Vincent Janssen. It is not just me - I try to score but we all try to score more goals."