Tottenham are unsure how long forward Son Heung-min will be out for with the foot injury he suffered in the

Premier League victory over Manchester City.

Son, 23 – who has scored three goals in his opening five games – was taken off with 13 minutes to go in the 4-1 win over the former leaders.

The South Korea international joined Spurs from Bundesliga side Bayer Leverkusen

for £22m in August.

Tottenham visit Monaco in the Europa League on Thursday.