Pierre is set to miss the majority of the rest of the season after an operation on Monday.
The 24-year-old picked up the injury against Blackburn Rovers in their 1-1 draw on December 23, in which he scored his first goal for the club.
Northampton’s manager Jimmy Floyd Hasslebaink said: “It’s a huge blow because he was playing ever so well. He was grasping what we wanted and we are going to miss his physicality.”
The boss has said his defender has the same injury as Aaron Phillips but expects his team to cope with the loss of Pierre, with other members of the squad expected to fill in.
He said: “You have to be flexible in this business and we have to adjust.”
Nemanja Matic believes Manchester United boss Jose Mourinho's driven methods and high expectations will bring the club more success.
Cardiff remain unhappy with Derby's decision to postpone Sunday's Sky Bet Championship game at Pride Park.