Interim coach Bruce Arians says Brown had surgery Tuesday and shouldn't miss more than two to three weeks.
Arians did not say which knee Brown injured in the victory over Green Bay, which apparently occurred on a 2-point conversion that followed Reggie Wayne's go-ahead touchdown catch with 35 seconds left in the game. Brown has 60 carries for 239 yards (4.0 average) and one TD.
Ballard has rushed for 42 yards on 21 attempts (2.0 average) this season.
Arians says a handful of other players are questionable for the Jets game. That list includes inside linebacker Pat Angerer (fractured foot), cornerback Vontae Davis (ankle) and outside linebacker Robert Mathis (sprained knee).
Information from The Associated Press was used in this report.