Gomes, 26, was tackled from behind by Son and appeared to be injured by an awkward fall which prompted an anguished reaction from players and fans close to the incident.
Former Everton winger Pat Nevin, who was the analyst for BBC Radio 5 Live at Goodison Park on Sunday, described the incident as "horrible".
"Players looked devastated and there was utter confusion - players with their heads in their hands," the former Scotland international said.
"Son was distraught before he was sent off, and Serge Aurier couldn't watch and was praying.
"Gomes was led straight to the corner to the ambulance to take him to hospital."