The attacker was taken off 34 minutes into the World Cup qualifier, having damaged his arm when he landed after a challenging Mohammed Musa for a header.
Son, 24, immediately went for medical treatment down the tunnel, and coach Uli Stielike admitted they feared the worst after the game.
"We have to have a scan, it may be broken," he said. "It's not good."
Fears were raised further when spokesman for the Korean Football Association said: "Son is suspected of having his arm broken. Our team doctor had the arm braced before being scanned when the team arrives back here this afternoon."
The extent of his injury is unknown as of yet, but his recovery could intrude upon Tottenham's preparations for next season once they return to training in early July, before embarking on their International Champions Cup campaign.
Former Bayer Leverkusen star Son scored 21 goals in all competitions for Mauricio Pochettino's side last season, netting 14 in the league for the runners-up.
Tuesday's loss leaves Korea second in their qualifying group, a point clear of third-placed Uzbekistan.