The popular Argentine is now back in the fold under Mick McCarthy, but he was dropped by Peter Reid and then Howard Wilkinson - leading to mass frustration.
However, he has recaptured his form and is now starring for The Black Cats.
"Last season was very difficult for me with injuries and not being in the team," he said.
"I think I only played six or seven games so I did not feel good about things.
"I was angry and disappointed last season and I thought I would have to leave Sunderland to make things happen for me.
"But since Mick McCarthy has been manager everything changed - straight away in the summer he told me he wanted me to be in his team.
"I told him `okay, if you want me to play for you then I don't want to leave - I am here and I want to play for Sunderland'.
"My opinion of him is very high - and I think things will be better for the future of Sunderland with him as manager because he knows what he wants from the players, knows how to get it from them and is very good for the fans too.
"I'll always be grateful to Mick McCarthy for the opportunity he gave me to prove myself in my proper position.
"He gave me the opportunity and he took all the pressure off me. You always want to play and my ambition is to play for my national team. If I am not playing there is no chance of that happening.
"I have been playing as a left back since I was eight or nine, and while it wasn't too different playing as a winger I think I have more space to use on the pitch from the back - I have the ball more and I can do more with it.
"Having seen me play there this season I hope both the manager and the supporters think they are seeing me at my best. But, of course, I have no excuses now!
"As players we must keep concentrating on doing our jobs well - it's been a good start for me personally and for the team and at times we have been playing very well.
"Now we must always try to improve so we can be promoted back into the Premiership."
