The 82-year-old entertainer told London's Southwark Crown Court that Clifford was always pleasant and friendly when he attended filming for the Des O'Connor Tonight show.
Clifford, 71, is standing trial accused of 11 counts of indecent assault against seven girls and women.
He denies all of the charges.
O'Connor, who hosted the Des O'Connor Tonight show from 1977 to 2002, said Clifford would visit ITV's Teddington studios when his client was appearing as a guest.
Asked whether he had ever witnessed Clifford acting unprofessionally, O'Connor replied: "Never. I don't think he would ever need to in any shape or form.
"He was just there to accompany his client if there was any problem."
O'Connor said that he had become friends with the publicist after he and his wife had been invited to charity functions in the early 2000s.
He said: "It impressed me he cared.
"He was genuinely, genuinely concerned about the illnesses of the children."
The former chat show host said that Clifford was "always pleasant, always charming".
He told the court: "I find it hard to imagine him being anything other than caring, concerned and generally good company.
"I can't imagine him being anything other than honest and with integrity.
"I always found him the man he appeared to be - pleasant, friendly, helpful, kind."
Concluding the defence case, Richard Horwell, QC, defending Clifford, pointed to the fact that it was agreed Clifford had "no previous convictions, cautions, reprimands or warnings".
The trial, taking place at Southwark Crown Court, continues.