The incident occurred in the game between Chichester and Wingate and Finchley on Saturday in the Isthmian League Premier Division. Reports have stated that his body twisted on the wet surface as he slid, causing his forehead to smash into the wall.
The 21-year-old was a part of the Gunners' U21s side up until last year, when he moved to Hastings United on a free transfer and Chichester have now released a statement on the striker.
"Billy received a significant brain injury and is currently in an induced coma in intensive care receiving the best possible treatment.
"It is too early to say what the outcome will be and even if things go well, there will be a long road to recovery."
Wingate & Finchley said in a message of their own: “Everyone at Wingate & Finchley continues to keep Billy, his loved ones and all at Chichester City in our thoughts. Wishing him strength on the fight to recovery.”
The match was abandoned following the incident, and updates are sure to come over the next few weeks surrounding his condition as messages of support flood in.