The Spurs skipper limped off late in the dramatic 2-1 derby defeat in north London, replaced by Argentine striker Alejo Veliz for the final exchanges after appearing to be dealing with discomfort for a few minutes.
Tottenham face a quick turnaround as they host Newcastle next in the Premier League on Sunday and can ill-afford to be without their influential forward as head coach Ange Postecoglou battles an injury crisis that has already deprived him of the services of the likes of James Maddison, Micky van de Ven, Rodrigo Bentancur, Ivan Perisic, Eric Dier, Manor Solomon and Ryan Sessegnon.
Chatting to Spurs' in-house media team after the West Ham game, Son said he hoped he had avoided an injury but would need to have it assessed.
"I hope so," he said when asked if he was doing okay. "I had a big kick on my back, in the back of the bone, so we'll see. I haven't had time to assess it so we'll see what happens."
Speaking to the Daily Express after the game, Son said: “No, I’m okay. I’m okay. Let’s see.”
Postecoglou was unable to offer an update on Son's fitness after watching his depleted side become the first in Premier League history throw away a 1-0 advantage and fail to win in five straight matches.
It was also the third consecutive home game in which Tottenham have taken the lead and not managed to see out a victory, meaning they have now dropped a whopping 16 points from winning positions already this term.
Asked if Son was okay after limping off on Thursday, Postecoglou - who did at least get Cristian Romero back from suspension against West Ham, with the Argentine on the scoresheet early before second-half efforts from Jarrod Bowen and James Ward-Prowse said: "I don't know. I'm not sure."