Our USA international goalkeeper will join up with the Saints today and will be included in their squad to face Portsmouth at the St Mary's Stadium tomorrow.
Southampton have been hit by injuries to their keepers and have been given special dispensation by the Premier League to sign Kasey outside of the transfer window.
Both Antti Niemi and Paul Smith - as well as fourth-choice Michael Poke - are recovering from injury and third-choice Alan Blayney has played in their previous two matches.
The move presents Kasey with an opportunity to get some first team football under his belt having been understudy to Paul Robinson in all but two of our games so far.
Kasey Keller has joined Southampton on a month's loan to help ease their goalkeeping crisis.