The Tottenham Hotspur boss doesn't just need the South Korean's quality, he needs the option to drop one of his struggling forwards.
There isn't much a manager can do if a player is injured. Maybe a word in the physio's ear about getting them back as quick as possible - not the kind of words Jose Mourinho may have had in mind when arguing with Eva Carneiro.
The energy Son has already given the north London side since moving from the Bundesliga is exemplary and he is the perfect Pochettino player.
It's not even so much about what the 23-year-old brings, however. It's about the Tottenham boss then being able to take players out of his XI.
Indeed, right now, Pochettino is more or less forced to play the struggling Nacer Chadli. The Belgian has been under-par and in need of a rest for some time.
And, once Son got firing, the Spurs boss was able to demote Chadli to the bench. After a few games out, he may well return the player he can be.
The South Korean's injury, though, has once again stripped Pochettino of that possibility. Who else can he play out wide? Mousa Dembele is only just returning from injury, Clinton Njie is still bedding in and Andros Townsend showed he is still the same old Andros Townsend against Swansea City.
Son provides options and his return will allow the Tottenham coach to give 26-year-old Chadli some time out. Based on his Swansea showing, he is still very much in need of it.