In joining the Saints, Osvaldo will be re-united with his former Coach at Espanyol - Mauricio Pochettino.
"He's magnificent," the former Fiorentina player said. "It's fantastic, great to work with him.
"He is a great motivator and for me it's very important to work with people who appreciate and respect how I work. For many years people haven't appreciated that.
"I know him well and how he sets out his teams. The season I had at Espanyol was my best as a footballer. In a personal sense, I think I did well playing under him.
"I want to repeat that and improve it. I'm confident that will happen and I can't wait to start."
For the big stories and the banter follow us on Twitter: @tribalfootball