Footballers were today warned that spitting could increase the risk of spreading swine flu as players at two Premier League clubs were struck down by the virus.
The Health Protection Agency (HPA) said the "disgusting" habit - a common sight at many matches - could lead to infections being passed on.
Blackburn and Bolton both have a number of players showing signs of the virus ahead of their Carling Cup matches this week.
The HPA said spitting should be discouraged by football clubs as experts attempt to halt the spread of the infection.
"Spitting is disgusting at all times. It's unhygienic and unhealthy, particularly if you spit close to other people," said a HPA spokesman.
"Footballers, like the rest of us, wouldn't spit indoors so they shouldn't do it on the football pitch.
"If they are spitting near other people it could certainly increase the risk of passing on infections.
"Certainly, spitting is a nasty habit that should be discouraged - and it should be discouraged by the football clubs.
"It's about setting examples for young people who idolise them."
He added footballers should follow the same guidelines as other members of the public by washing their hands, covering their mouth when sneezing and disposing of used tissues.
"The advice is catch it, bin it, kill it," he said.
The Football Association and Barclays Premier League said they were following guidance from health experts in handling the issue.
"As ever, when it comes to health matters the Premier League will be guided by the relevant statutory authorities," said a Premier League spokesman.
Chelsea coach Carlo Ancelotti gave his squad a clean bill of health after their victory over Blackburn last Saturday was overshadowed by cases of swine flu among the Rovers squad.
The Blues were told Blackburn had a problem with the H1N1 virus the day before their clash, but Ancelotti is unconcerned some of his players may yet develop flu-like symptoms.
"I'm not worried," said Ancelotti. "The flu is not only on the pitch, it's everywhere. We take all the precautions and we want to think about playing, that's it.
"We are not worried about this problem because we've taken all the precautions."
Bolton travel to Stamford Bridge for their Carling Cup fourth-round tie tomorrow but manager Gary Megson - who has already seen four of his own players come down with and recover from the virus - was not concerned about it spreading during a match.
Asked if he was worried about his players coming into contact with Chelsea's, Megson said: "Not from that perspective because I've heard varying opinions.
"I think the one we all need to listen to is that from the medical people, who are saying that it is very difficult, if not impossible, to contract it in that way.
"They are all okay at the moment but it wouldn't be right to start giving you names."
Manchester City manager Mark Hughes believes most Premier League stars are capable of recovering from swine flu in a matter of days.
City defender Micah Richards was struck down while on holiday in Cyprus in the summer.
Hughes said: "What you find with Premier League clubs is that there are a lot of young, fit, energetic guys.
"If they do get it, they are only laid low for a couple of days. They soon get over it because they are fit and healthy and are not compromised too much."Reuse content