He was rushed to hospital during the club’s 0-0 National League North draw with Southport on Saturday.
The on-loan Chesterfield left back collided with a Port player and was immediately taken in for treatment.
Darlo have been informed about the true intent of his injures and the news is not good.
Muggleton has a fractured femur, ruptured anterior cruciate ligament and ruptured posterior cruciate ligament.
In addition the player has ruptured his lateral colateral ligament and has picked up a tear on his knee tendon.
The club hope to see him back on the field at the earliest opportunity possible.
“Obviously, he is going to need an operation and further medical treatment, and so we would like to wish him well, and a speedy recovery,” the Quakers said.