Jamaal Lascelles' header from a corner gave the Magpies the advantage, but a scrappy own goal from the unfortunate Karl Darlow saw the Clarets come away from St James Park with an undeserved point.
Defour wasn't the only key player missing as James Tarkowski has also suffered an injury.
Dyche said: “Defour will have to have an operation after seeing a specialist, it’s a real blow. It’s come out of the blue, he’d been playing on and felt a soreness in his knee, he played with it for a few weeks.
"We took him for a scan, one of those ones you probably wish you wouldn’t have now, and it showed something that needs doing, it’s a bit of cartilage. That’s the way it goes."
Asked if Defour would return before the end of the season, Dyche added: “I don’t know yet, we’ll have to wait and see.”
He offered a far more optimistic review of Tarkowski's injury though, saying: "Tarky we’re a lot more hopeful on, we’re hoping his will settle down sooner rather than later. It’s a groin situation, hopefully that will settle."
Burnley's extensive injury list also includes star striker Chris Wood and left-back Stephen Ward, but their January business left a lot to be desired, bringing in just two reinforcements.
Dyche admitted his club struggled to compete, saying: "There was a couple of situations we thought might come our way, but the market is tough, we all know that. We are what we are, everyone knows that, we have to run the club in an appropriate manner and that’s what we chose to do and that makes it difficult.
"There’s certain situations where the money goes up and up and up and eventually you have to say no, not for us. It is what it is, we move forward but I’m pleased with the other bits of business with Aaron (Lennon) and GK (Nkoudou) coming in."