The Manchester United centre-back pulled out of the Three Lions squad for games against San Marino and Montenegro because of his need to observe an "intricate pre-planned training programme".
But Campbell sympathises with his former England team-mate and does not blame Ferdinand for refusing to add extra matches to his schedule.
"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.
|5/1||Wayne Rooney is 5/1 with Paddy Power to score the opening goal in Montenegro v England
"It is physical, because it is demanding international football - and the travelling as well. If you have your regime and way of playing and routine, then playing for your country, there is a lot in it.
"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."