Roberto Di Matteo refused to condemn supporters who shout unacceptable abuse from the stands as he suggested it was commonplace at every stadium and had been for years, citing the example of his former Chelsea team-mate Graeme Le Saux, who routinely endured homophobic chants.

Di Matteo's addiction to noncommittal answers led him into dangerous territory before the Premier League fixture against Manchester United at Stamford Bridge, when Rio Ferdinand could face hostility when he plays for the visitors over the support that he showed for his brother, Anton, in the John Terry racist slur saga. Ferdinand heard his every touch jeered in the corresponding fixture in February.

Chelsea's players are set to wear Kick It Out T-shirts on Sunday and it was put to Di Matteo that, with emotions running high after Terry, the Chelsea captain, accepted a four-match domestic ban for racially abusing Anton Ferdinand, he might not want to see the booing of Rio Ferdinand. Di Matteo's answers, though, were shaped by a determination not to be seen to be criticising any Chelsea fans.

"I don't know how every single supporter will react," he said. "Generally, our fans have been very respectful and very good in their behaviour. Don't forget, we get booed as well when we go away from home. It's not just focusing on our supporters. Our supporters have been generally very good.

"Hopefully, they will cheer us on and try to push us to win the game, more than anything."

Di Matteo's reluctance to make a strong statement on offensive chanting was curious. "I think you get that in every stadium," he said. "It's happened with many players before. I remember when I was playing with Graeme Le Saux, he used to get booed a lot so … Some people feel that's right and some don't."

Di Matteo was also asked whether Chelsea would support the Professional Footballers' Association's six-point plan to combat racism, drawn up in the wake of the Terry scandal, which would see players sacked for racist abuse.

Chelsea fined Terry, who will use his programme notes on Sunday to state his support for the Kick It Out campaign, but did not consider dismissing him.

"It's a difficult one," Di Matteo said. "If the majority believe that we need a law like that then we will obey it and support it. If it will become a rule, we will play by the rules, as we have always done. As a club, we are against any kind of discrimination and, if it does go through, then we will support it."

Di Matteo described the United fixture as one of the season's "classics" but he will be without Frank Lampard, who has a calf strain that will rule him out for three weeks.