The charity Keep Britain Tidy has asked footballers to stop spitting as young people are copying the habit.
Many fans were upset by the Bolton striker's spitting incident
The group, based in Wigan, Greater Manchester, criticised players for making a "filthy habit appear macho".
In a poll of nearly 300 fans, 75% said they were upset by the incident when Bolton striker El-Hadji Diouf spat at Portsmouth player Arjan de Zeeuw.
Manchester United boss Sir Alex Ferguson was also mentioned for spitting out chewing gum after matches.
'Spreading the flu'
Alan Woods, chief executive of Keep Britain Tidy, said spitting was the ultimate insult, and "a contemptuous gesture drowning in hate."
He added: "But it is not just revolting - it has a cost.
"Saliva and chewing gum deposited on the pavement needs to be washed and cleaned-up and when it is aimed at another person, spit can spread colds, flu, measles and mumps."
To encourage footballers to stop spitting, Mr Woods is writing to the Professional Footballers Association, to say why he thinks players should set a better example.