The goalkeeper ended an eight-year spell with Villa to join newly-promoted Boro on Friday.
Aston Villa manager Roberto Di Matteo has told reporters, as quoted on the club's official Twitter account, that he wishes the best of luck to "loyal" goalkeeper Brad Guzan following the American's move to Middlesbrough.
Guzan has departed Villa Park after eight years with the Birmingham club to take up a new challenge at the promoted side after falling out of favour.
The American international spent the majority of the first half of his time in England as a back-up goalkeeper to number one stoppers such as his compatriot Brad Friedel.
However, in the last few years he made the spot his own, and though he was dropped for the final weeks of last season, he departs the club having made 169 competitive appearances in all competitions.
Guzan has now moved to Middlesbrough to compete with the likes of former Barcelona star Victor Valdes and veteran stopper Dimi Konstantopoulos for the number one shirt at the Riverside.
Di Matteo, who only took over at Villa after Guzan had already fallen out of favour, wished the USA man all the best in his future career, and was quick to highlight the loyalty and commitment shown to the club by the goalkeeper over the years.
The Italian boss said, as quoted on the club's official Twitter account: "Brad has had a really good time here. He's been very loyal.
"As in life, everything has a start and an end. We wish him good luck."
Guzan had become the subject of much criticism from Villa fans in recent times due to often terribly inconsistent form and a number of high-profile errors.
Few supporters will mourn his exit, particularly with the arrival of young Italian stopper Pierluigi Gollini this summer, but the club have nonetheless lost a man who served them well over the best part of the last decade.