The winger penned terms to 2016 yesterday.
"It's great news that Jason has agreed to sign a new contract with Southampton," the Saints manager said.
"He has been very impressive for the club this season and especially so since I arrived, and he is a very important member of our squad.
"He has responded really well to the challenge of the Premier League and is clearly playing some of the best football of his career, so it's really pleasing that he is staying here.
"Jason is a determined and passionate person, and that honesty and emotion has transferred into his performances and so he fully deserves this contract extension.
"I was never in any doubt that he would like to remain at Southampton, and I am looking forward to seeing even more from Jason over the next few years."