"Jack has continued to train with the under-21 squad and won't be included in the squad for Southampton," Garde told reporters at his pre-match news conference on Thursday.
"I have a date in mind for when I will bring him back but that will remain private."
The defeat by Watford left Villa rooted to the bottom of the table on five points, with 11 defeats in 14 league games so far, and Garde called on his struggling team to stop making errors.
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"We are in a big competition and have a tough job to do. To achieve what we want to do we have to be 100 percent focused," he said.
"We know that we have to win games. We didn't win the last one. It was a disappointment. We made too many mistakes and conceded too many goals."
The manager is hoping to kickstart the fight to stave of relegation against Southampton, but is expecting a tough game from opponents who will be looking to bounce back after being knocked out of the League Cup by Liverpool on Wednesday night.
"Southampton is a good club. It will be of course a tough game for us. The defeat (by Liverpool) was hard for them and they will probably be looking for revenge on Saturday and we will be prepared for that," Garde said.
The manager also confirmed that striker Gabriel Agbonlahor could play a part against Southampton after returning to first-team training for the first time since picking up a calf injury in early November.
(Reporting by Simon Jennings in Bengaluru; editing by Sudipto Ganguly)
