The Tykes suffered a 3-1 defeat against Middlesbrough at the Riverside Stadium to leave themselves five points adrift of the relegation zone with just a game left to play.
"It's been a pattern and we've not scored enough goals. That's been the main problem. It's a horrible feeling," the club's official Twitter page quotes him as saying.
"You can't fault the boys. Certain times in the game you need that quality in abundance and we haven't got it in key areas. There will be a lot of changes, I'm sure, but it'll be for the better.
"We will start planning for next season. The boys are hurting like mad. One thing is very clear - it needs starting again. To prolong it for so long when we were constantly written off is a credit in itself. It'll take a bit of getting over but we will."
Barnsley will join Yeovil Town in League One, after the Glovers were relegated following last night's 2-0 defeat against Brighton & Hove Albion.