The 23-year-old has been on loan with George Burley's Saints since October and he has impressed in his 12 displays.
There were some suggestions that Southampton could not afford the £1million deal - but Burley has confirmed he wants him to stay.
"Andrew is 23 and for me there's no doubt he's got Premiership quality," Burley told the Daily Echo. "He's shown he's an excellent defender who is good in the air, strong and competitive.
"To get a young defender like this would be great - it's very important for the future of the club."