Champions City climbed into third position, behind second-placed Liverpool, after Kevin De Bruyne's deflected goal in the 81st minute claimed a point after Liverpool had twice taken the lead through Sadio Mane and Mohamed Salah.
But the game was marred by the spitting incident, which left Guardiola urging Liverpool to take action against anyone found to have been involved.
"They [the staff] told me, but I didn't see it," Guardiola said. "In every club there are people like this. Some can't control their emotions.
"I am pretty sure Liverpool FC will take measures against this person. I know that Liverpool is greater than this behaviour.
"I am sure they will investigate it. Like when they smashed up our bus. It's always a pleasure coming to Anfield."
Liverpool have confirmed they are investigating the alleged incident.
City's visits to Anfield have previously been impacted by crowd disorder, with the team bus attacked by fans en route to the stadium prior to a Champions League quarterfinal in April 2018.
On that occasion, windows on the bus were smashed by objects such as beer bottles and stones, forcing the City players and staff to lie on the floor and between seats to avoid injury.