Hi and welcome to the forum
That is not hole in the head disease.
Is the eye still there and covered with a white film, or is the eye ball missing?
If the eye ball is missing, the fish has had its eye eaten by the cichlids.
What cichlids do you have and what other fish are in the tank?
Keep the pleco separate from now on and feed it well on a variety of foods.
Make sure you have some driftwood in the tank for the pleco to graze on. they need the fibre to help their digestion.
Do a 75% water change and gravel clean the substrate every day for a couple of weeks. This will help reduce the chance of infection.[/QUOTE
Thanks for your quick response - I have attached another photo. I believe his eyes are still there. The holes are on both sides of his head. There are 10 African cichlids in the tank with him and as of now, I have removed him from the main tank. I will add a piece of driftwood to the tank and replace the water. I do hope it helps.