Stuart Gray said the Owls need to address their Jekyll and Hyde nature if they are haul clear of the Championship drop zone.
Saturday’s home defeat to Bournemouth saw Wednesday deliver a converse performance when compared to recent displays against Leicester and Watford.
And Gray said: “We are a Jekyll and Hyde team at the moment and that is the most disappointing thing.
“We prepare the players for the best possible performance but we are so inconsistent at the moment.
“I thought we started brightly but heads went down after they scored their first goal. The defending was schoolboy and we won’t win football matches defending like that.
“In the end we finished the game the stronger and got a goal back through Jacques but it was too little too late from our point of view.”
Problems continue to mount for the Owls as the treatment room is bursting at the seams.
Connor Wickham (hamstring) and Glenn Loovens (back) were sidelined for the Bournemouth loss and Atdhe Nuhiu is now another addition.
Gray said: “It looks like Atdhe has popped a shoulder and we’ll have to wait and see how bad it is before we play Blackburn on Boxing Day.
“It’s the same for Connor, he tweaked a hamstring in the Wigan game and didn’t come through a fitness test on Friday.
“Hopefully, he will be OK for Boxing Day.
“So we have too many in the treatment room and we need those players back as soon as possible.”