Johnson commented: "We're disappointed with the game last weekend, we're disappointed with the way we played, there's no other way of saying it.
"There won't be any kneejerk reactions here though, we can't change everything we are trying to do here on the back of one game and one poor performance, that would just be crazy and would get us nowhere in the long term. If you look at results so far this season, not just in the Magners but in England as well, other sides have had disappointing results already, but those teams aren't tearing everything up and starting again, and neither are we."
He added: "The reality is, we're trying to change a couple of things, and we've got to get better at doing what we want to do. We're trying to move it in a different direction and we're trying to find an identity that's us.
"We've had a lot of guys coming back at different stages and it's not quite embedded in the squad as we'd want yet. Old habits die hard really, so we've got to find our level and where we need to be as a team, so we're a work in progress.
"We can only do it by doing it more often, and doing it better. That's where we are - we aren't happy where we are but that's where we are. If we can acknowledge that we let ourselves down, then that means we've let the people who support us down.
"At the end of the day, it's not through lack of energy, or lack of intent, but we've got to get our part right. We know that we've got to be at a certain destination at a certain time, we could take the easy way, or we could take the hard way and try and get the outcome we desire, and that's the route that we've decided to take.
"If we felt that what we are doing was right for us last week, then it's still the right way for us now, one game doesn't change that. We've got to keep things in perspective and realise that we've only lost one game.
"The reaction since Saturday has been good one we are looking to move forward from that. Leinster at home on Friday night is the ideal challenge, they are tough opposition, but you've got to get back on the horse straight away.
"We've made some changes as we're looking to get players up to speed and into the squad and a few more boys will get some game time this weekend, some will come off the bench, and with a short turnaround this week we've had to change things around a bit in terms of personnel. We had a good idea of the shape of this team last week, it's all part of what we are trying to do, building up week by week, and managing the squad over a long season."
The clash will see centre Andrew Bishop make his 100th Ospreys appearance while Wales full back Lee Byrne makes his first appearance following the British & Irish Lions tour to South Africa. Fellow Lion Tommy Bowe makes his first start after coming off the bench last Saturday, while Alun-Wyn Jones is named among the replacements.
Nathan Hines and Eoin Reddan will make their first starts for Leinster. Scotland international Hines partners Malcolm O'Kelly at second row, while in the front row Stan Wright lines up alongside Cian Healy and John Fogarty.
Ireland scrum-half Reddan partners Jonathan Sexton in a backline which also sees Gordon D'Arcy come in for his first start of the season. The back three of David Kearney, Shane Horgan and Isa Nacewa remains the same from the one that started last weekend's 23-14 victory over the Dragons.
Ospreys: 15 Lee Byrne 14 Tommy Bowe 13 Jonathan Spratt 12 Andrew Bishop 11 Nikki Walker 10 James Hook 9 Jamie Nutbrown; 1 Duncan Jones 2 Huw Bennett 3 Craig Mitchell 4 Ian Gough 5 Jonathan Thomas 6 Jerry Collins 7 Marty Holah (capt) 8 Tom Smith
Replacements: 16 Richard Hibbard 17 Paul James 18 Alun-Wyn Jones 19 Filo Tiatia 20 Mike Phillips 21 Dan Biggar 22 Gareth Owen.
Leinster 15: Isa Nacewa 14: Shane Horgan 13: Gordon D'Arcy 12: Shaun Berne 11: David Kearney 10: Jonathan Sexton 9: Eoin Reddan; 1: Cian Healy 2: John Fogarty 3: Stan Wright 4: Nathan Hines 5: Malcolm O'Kelly 6: Kevin McLaughlin 7: Shane Jennings (capt) 8: Sean O'Brien
Replacements (from): Bernard Jackman, Mike Ross, Leo Cullen, Devin Toner, Stephen Keogh, Chris Keane, Fergus McFadden, Simon Keogh