The 20 year old midfielder is being punished after being pictured in a nightclub following the 4-0 defeat at Everton almost two weeks ago.
Garde said: "He has trained this week with the under-21s because it was the plan. He knew that. I know when he might return, he knows as well and when he will I will tell you.
"Like every player Jack made a mistake and he has to pay the consequences for that. If another player does something wrong he will have the same treatment.
"Jack is young and will be back because when he is fully committed in his job he will be a good player."