He could miss up to five Spurs games while at the international tournament in the United Arab Emirates, which ends with the final on Friday, February 1.
Son is hoping he can sign off in fine fashion with a victory over Ole Gunnar Solskjaer's in-form United side at Wembley, per Sky Sports' Jack Wilkinson:
"It's not easy for me to leave the team at this important time. I feel very sad and sorry, but I want to win this game and go with confidence to Dubai. To play for your country is always a proud moment, but it's tough for me having missed one month of the season already. I want to go with three points, with confidence to Dubai."
The 26-year-old missed a month of Spurs action at the beginning of 2018-19 to win the gold medal at the 2018 Asian Games.
Upon his return, he took some time to hit top form—he had also played a key role in South Korea's FIFA World Cup campaign—but he has been fantastic of late:
As such, it will be a big blow for Spurs to lose Son, especially as they are still in the Premier League title race.
While he is away, he could miss Premier League matches against Fulham, Watford and Newcastle, the League Cup semi-final second leg against Chelsea and a visit to Crystal Palace in the FA Cup fourth round.
All are winnable games for Spurs even without Son, but the knock-on effect of a heavier workload for all involved could be more significant.
Son is clearly eager to sign off on a high note against United, but it is a much tougher fixture now than it perhaps would have been a month ago.
United are in flying form having won five from five under Solskjaer following Jose Mourinho's sacking, and the Norwegian will be keen to earn the biggest win of his tenure so far.