Ralph Hasenhüttl confirmed Romain Perraud missed out against Liverpool with a fracture, although the full-back is not expected to be sidelined for the long-term.
Perraud, who has enjoyed a good debut season in the Premier League, was one of five changes from the side that had played Brentford in the team's previous match, although his absence was an enforced one.
"He has a fracture in foot, and he is out for five to six weeks," said Hasenhüttl.
The Saints boss was also without goalkeeper Fraser Forster for Tuesday night's game, detailing the reason behind his injury.
"Fraser had back problems this week and was not ready to play today," he said.