This will keep him out of action for six months and regrettably means he will not be fit for selection by the English national team at this summer’s FIFA World Cup in Brazil.
The 24-year-old has already been scanned and has met with a specialist knee surgeon. He will be having a routine operation shortly.
The Club will post any further updates once Jay's rehabilitation is underway.
Les Reed, Director at Southampton Football Club, commented: “Jay is naturally disappointed, but is determined to get back playing for Saints as soon as possible.
“Everything will be done to return him to full fitness and deliver a speedy recovery.
“Jay has asked us to pass on his gratitude to everybody who has shown him their concern and sympathy during the 48-or-so hours since his injury.
“Everyone at the Club now wishes Jay well and we will support him, along with his family, to ensure that an international career plays a big part in his future.”