"People have to talk and work it out. I think it was a shock to Rio," Campbell told the Mirror. "He was probably thinking he didn’t have a chance and then all of a sudden he has a chance. It was kind of surprising. I know what Rio is going through, the extra matches do take a lot of out of you."
The Manchester United center back pulled out of the Three Lions squad for games against San Marino and Montenegro because of his need to observe an "intricate preplanned training program."
But Campbell sympathizes with his former England teammate and does not blame Ferdinand for refusing to add extra matches to his schedule.
"If you haven’t put that into your routine or if no-one a month ago has told you: ‘I am thinking about putting you in’, it is hard. It is a critical moment for England and a critical moment for Manchester United so it is hard for him," Campbell said. "It is physical, because it is demanding international football - and the traveling as well. If you have your regime and way of playing and routine, then playing for your country, there is a lot in it."
He added, "If you are in your routine and all of a sudden you have to look into playing another game - it is demanding on the body. The demands on the body playing for England can be a lot. But I think he would love to be involved in the next one."