Former England boss Eriksson admitted his disappointment at the situation.
"I am very disappointed, very much so because we signed him and we thought we should have him for longer," the Swede said.
"Yes a little bit (let down), but I think everybody has the same feeling - the players, the coaching staff, the directors and the fans because he is a big name and an important player.
"I really don't know the real reason. He didn't like the training pitch and the dressing room and things like that, but he knew that before because we showed him around before he signed.
"We know we are not perfect at this moment and I don't think that would be fair at all. It is a long-term project.
"Since the new owners came in, the club has signed seven or eight new players, and you can't build a new training ground in four or five weeks.
"It takes time to make the stadium better, it can't be done over a weekend so I think that's unfair.
"We are all sorry that he has gone but the project goes on without Sol Campbell, nothing has changed."