Manchester United boss Sir Alex Ferguson has warned against allowing media personnel in to watch club training sessions.

United's title rivals Manchester City were involved in a controversial training ground incident yesterday, with pictures appearing to show manager Roberto Mancini and enigmatic striker Mario Balotelli clashing.

Ferguson insists that a similar incident would never happen at United as he wouldn't let the press into his training sessions, and doesn't understand why other clubs do.

"You are protecting the possibility of success. Do ICI send an email to another bio chemicals company telling them their new discoveries in drugs? Does any major company tell its opponents what they are doing? I am sure they don't," said Ferguson.

"Unfortunately football has a media profile which means cameramen want to be at training sessions. I think that is ridiculous but it makes it very difficult for a coach to do their work because you don't know where the information can go.

"I think it stopped at Real Madrid under Jose Mourinho, but there are some places where the press are in every day. This is what they expect. I know it happens in Italy. I don't know how you can do your tactical work. Fortunately, at our place, we can guard against it to a decent degree."

Seven points currently separate the Manchester clubs in the league table, with United leading the way.