Both players rose to meet a Dirk Kuyt cross in the lead-up to the incident, which left Smalling and Huntelaar lying in pain on the pitch for some minutes. The Manchester United defender was subsequently taken to hospital for medical experts to assess the extent of the damage.
Interim England manager Stuart Pearce confirmed Smalling was able to communicate with England medical staff before being taken away.
"Chris Smalling has a really bad gash on his head and I believe he's gone to hospital so I hope that's not too bad," he said. "I spoke with him and he was conscious. Our thoughts are with him and I am hoping that he will be fine."
Manchester United and England team-mate Ashley Young said: "Obviously it's not too nice to see him go off in the way that he did. Hopefully, he's going to be all right.''