The forward will return to his parent club Barnsley to undergo the surgery and preliminary stages of his rehabilitation and is likely to be out for six-to-nine months of the season.
Ash has sustained injuries to both his anterior cruciate ligament and his meniscus and despite showing positive early signs, will in fact need to undergo surgery on the injuries.
The surgery will take place at the end of August.
On the news, Wood manager Luke Garrard commented: “I am gutted for Brad, he is a fantastic lad and was a delight to have around the club, his energy and positivity gave everyone a buzz.
“I know what the boy is going through, I suffered the exact same injury and it is a tough time for a player, but he will receive first-class treatment at Barnsley.
“He had been excellent in his short time at the club and played a key role in our pre-season, but he will return a better and stronger player for the experience.
“Both myself and everyone at the club wishes him all the best”.