The Spurs midfielder will return to his parent club for treatment but Premier League regulations say the Midlands club have to pay his wages for the duration of the season-long loan.
Villa manager Alex McLeish told reporters: "I think you do an agreement with a club and you take that on as far as the agreement goes.
"The club which takes him on loan has to fulfil that agreement. Jermaine will go back to Tottenham but we've still got an agreement with Tottenham."
He added: "We can only sign one more loan player in January now because Jermaine still counts. We've got to look at that rule."
Jenas has been plagued by a series of injuries since making the switch to Villa, including a groin problem that kept him out for the first two months of his arrival.
He has played just 108 minutes of football in a claret and blue shirt for McLeish and it will cost Villa chairman Randy Lerner approximately £1.3 million plus medical bills for the injury sustained by the 28-year-old against Manchester United.
McLeish has other injury worries with goalkeeper Shay Given expected to miss one month of football following the hamstring injury he picked up in the same game.
How do you stay up to date with football when on the move? With http://m.goal.com – your best source for mobile coverage of the beautiful game.