"It is a big few weeks for us," he said. "We shot ourselves in the foot against Biarritz and then we did not play well against Aironi, although we did what we had to do to get the five points.
"We have to win all our games now. We lost a home game and history shows that if you win your home games and pick up some points away from home, you're likely to go through. We've lost that first home game and that means we need to pull a win out of the bag away from home to claw that back before nailing our home games.
"These next two games will decide whether us or Ulster will challenge Biarritz to go through. So this game is like a semi-final for us.
"Biarritz are in the driving seat because they beat us away from home and they picked up points against Ulster. If we lose at Ravenhill it will make life incredibly hard for ourselves. We've already made things tough but that would make it a really uphill task.
"Ulster are a good side. We've got consecutive games against them which means both teams get to know the opposition well and a good couple of games in the Heineken Cup can really push you on.
"They are a very dangerous side who are capable of an awful lot of things with the players they have so it will be a huge task for us.
"Playing a team one week after the other can be an advantage but if they get some momentum up on you in the first game, it makes life very hard. So that first game is a really important one - I suppose the advantage we have is that we are going away and the pressure is on them - but it's not easy going there, the crowd are pretty loud and it can get pretty cold there as well."
Barkley, who had a season with Gloucester Rugby, insists Bath are successfully going about the business of getting that expansive style back into their game.
"We are missing a lot of our width which we had last year and that caused problems for defences across the field," he said.
"Teams never really quite knew where we were going to hit them and that was an advantage. We seemed to find ways of creating that width and we're looking at doing that at the moment.
"Having width means that you're able to be more direct because defenders spread out to defend you, and if they don't, you just go round them. It sounds very simple but that's the theory behind it. As a distributor who plays at inside centre I definitely have a say in that but it's not something that's black and white. We all talk about it, we understand why it works for us and why it's very dangerous for us.
"Hopefully, we'll get Butch James back in one of those two games and we've got all our international boys back now. It's a huge boost having them back. To go into these big games with those six players back is huge for us. They're all quality players and they'll lift everyone else around them.
"Heads have not dropped. We are just not clicking as a side and have been shooting ourselves in the foot a lot. If we can cut out our errors, there's no reason why we can't start that run now and not in January."