Barnard could make his Southampton debut in Saturday's FA Cup fourth round clash with Ipswich Town.
Meanwhile, Southend have signed Saints striker Matt Patterson on a free and extended Wolves defender Scott Malone's loan deal until the end of the season.
Patterson, 20, has signed a two-and-a-half-year deal at Roots Hall.
Malone, 18, initially joined the Blues in August and has made eight appearances.
Source: BBC Sport
Source: BBC Sport