The recently-appointed Pompey boss, having suffered a second successive loss since taking charge, questioned the mindset of the players he has inherited and whether they deserved to be donning the shirt of such a big club.
More than 1,300 travelling fans witnessed another poor performance and Barker was not about to offer any excuses.
"It can't be coincidence that over the last eight or nine weeks there have been no wins and it's the same players involved, even if there is a different manager," he said.
"If you can't change the mindset of people perhaps you have to change the people and we will have to look at that during the January transfer window.
"We have a fantastic football club with wonderful support. Unfortunately, I'm not sure the players realise how lucky they are to be playing for such a good club
"I thought we were the better team in the first half, but games last 90 minutes and Bristol were probably good enough in the second half to deserve to win the game."