Huntelaar and Smalling hospitalised after clash
Huntelaar netted with a powerful header into the roof of the net after 59 minutes but smashed into Smalling, who went up for the same ball.
The two lay on the Wembley pitch for some time before Smalling was carried away on a stretcher and Schalke 04 striker Huntelaar walked off holding a bandage to his face.
Dutch coach Bert van Marwijk told reporters: "Huntelaar has gone to hospital because we think he has some damage there [to his head] but we don't know for sure.
"He looked better in the dressing room than on the pitch, but we have decided to have him checked out."
England's interim coach Stuart Pearce said Manchester United defender Smalling had also gone for a check-up.
"Chris went to hospital. I spoke with him and he was conscious, but he split his head open. Our thoughts are with him and I am hoping that he will be fine."