The 28-year-old penned a three-year deal with the Red Devils on Saturday, keeping him at Old Trafford until 2018.
"I'm really pleased Antonio has signed a new contract. His contribution to the team since he joined the club in 2009 has been fantastic," Giggs told United's official website.
"Antonio is a very powerful player with great speed and versatility. He is very professional in his approach to training and I am delighted he has committed his future to the club."
Valencia joined United from Wigan Athletic five years ago.