Carlsey collided with a concrete perimeter fence in the 15th minute, and was knocked unconscious for 20 minutes.
He was whisked away in an ambulance, but fortunately was discharged later that night.
Reynolds now says his medical team have recommended the forward miss 14 days of action to recover from the concussion.
The Brig boss says the summer signing from Longridge will be badly missed, as they prepare for a trip to title favourites South Shields, but that the striker’s health is the club’s priority.
He said: “Obviously his injury was horrible. He collided into one of the concrete pillars and he did not move.
“One of our players Stu Vasey put him in the recovery position and he was taken away in an ambulance.
“Fortunately he was released from hospital on Saturday night. He’s had severe concussion and it could have been a lot worse.
“We are delighted he is going to be okay. He has been a massive player since his arrival and we were badly affected by his injury on Saturday.
“We missed his presence but also it had a mental impact on the players on the pitch, it is not nice to see a team mate taken away in an ambulance and not knowing what is going on. Our medical team say it will be 14 days until he can return to football but we will see.
“We are just thankful he is okay, it could have been so much worse.”
Brig now face a trip to Ashton Athletic in the first FA Cup preliminary round.
And Reynolds praised super-sub Jamie Milligan for getting them to the next round as their performance was impacted by the horrific injury.
He said: “I’m not going to mask over it, we got through due to two moments of brilliance from Jamie Milligan. He is an exceptional player.”
and it is credit to Jamie that we are in the next round.
“I don’t think any other player at the club could have scored his first goal and having a free-kick for him is the equivalent of having a penalty - I’d back him every time.
“It got to 60 minutes and I said to my assistant Simon Wiles Jamie is the person that can get us back into the game and he did.
“It is nice to see that we have options, strength in depth and players that can come off the bench and make an impact, we have got a really good squad and I am excited about the season.
“We now have to take that momentum to South Shields, they have won three out of three and it will be a tough test but we are going there to try and get a result”