New boss Ronald Koeman was clearly not satisfied with his current options that include veterans Boruc and Davis plus inexperienced Gazzaniga and he decided to make a move on the England international.
After having an initial bid rejected for Forster, the Saints appear to have agreed a £10 million fee with Celtic, while the player accepted their contract offer.
And with the 26-year-old now set to undergo a medical at St Mary’s, the transfer should be completed during the weekend.
Fraser Forster joined Celtic from Newcastle, who are entitled to 25% of the transfer fee, and went on to make 140 league appearances for the Bhoys.
Some impressive displays in the Champions League saw him attract interest from Barcelona, among other clubs, but Southampton were the first side to make an official bid for his services.