James McPake will have surgery on Tuesday after a hospital scan confirmed that the Dundee defender fractured his kneecap during Saturday's city derby.
The Scottish Premiership club stated that: "Following the surgery, we will have a clearer picture of timescales for rehab."
But it is highly unlikely that the 31-year-old will play again this season.
He was injured in a challenge with Dundee United midfielder John Rankin during a game won 2-1 by Dundee.
McPake was carried off on a stretcher and taken immediately to hospital.
"We would like to acknowledge the professionalism from both sets of players during the derby match on Saturday who immediately helped when it was clear James was in significant pain," added Dundee's statement.
"James is a vital part of Dundee Football Club and we wish him a speedy recovery."
Capped once by Northern Ireland, McPake has been at Dens Park since leaving Hibernian in 2014 and has previously played with Coventry City and Livingston.
Meanwhile, striker Craig Wighton has returned to Dens Park following his loan spell with Raith Rovers.
The 18-year-old scored once in 21 appearances for the Scottish Championship side.
He started 10 times for the Kirkcaldy outfit but in recent weeks has been on the substitutes' bench.