WARNING: Some viewers may find the incident, included in Darlington's highlights video below, upsetting
The left-back, out on loan with Darlington, had a coming together with Southport midfielder Marcus Wood, and suffered a partial fracture of his femur as well as knee ligament damage caused by a dislocation.
As Muggleton strode forward Wood moved to intercept and as the two players collided, Muggleton's left leg slammed into the Southport man.
According to Darlington, Muggleton is due to have further scans today to assess the full extent of the damage.
Muggleton was one of two Quakers players taken to Darlington Memorial Hospital with injuries sustained in the game.
A club statement said: "Sam Muggleton and Terry Galbraith were both taken to Darlington Memorial Hospital for treatment after sustaining injuries during Saturday’s home game with Southport.
"Sam has sustained two injuries – a partial fracture of his femur, and knee ligament damage caused by a dislocation. He will be having a further scan on Monday to assess the extent of the damage.
"Tez has suffered a partial concussion, and will be ruled out of Wednesday’s home game against Brackley.
"We’re sure that everyone connected to the club would like to wish both players a speedy recovery, and we would also like to thank the medical staff for their care and attention during and following both incidents."