Aidy Boothroyd has labelled the England U21 job as "utterly impossible" and defended the Young Lions' selection policy.
England need to beat Croatia by two goals on Wednesday and hope Switzerland lose to Portugal in order to reach the Euro 2021 quarter-finals in the summer.
They have had just one shot on target - none from open play - in their opening defeats to Switzerland and Portugal in Group D.
How can England still qualify?
- If England beat Croatia and Portugal beat Switzerland, then England, Croatia and Switzerland will be tied on three points each.
- UEFA's tie-breaker in that situation looks at the head-to-head record between the three teams. Each team would have won one and lost two against the others.
- Goal difference would next be used to split the teams. If England win by two goals on Wednesday, their GD in head-to-head games will be +1, Switzerland's will be 0, and Croatia's will be -1.
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Since being runners-up at the 2009 European Championship, England have qualified from the group just once - under Boothroyd in 2017.
Jude Bellingham, Mason Mount, Jadon Sancho, Phil Foden and Trent Alexander-Arnold could have all been included in the squad in Slovenia but Boothroyd insisted the senior team remains the priority.
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"I know the senior men's job has been called the impossible job but the U21s is the utterly impossible job," he said. "The reason is the amount of players who have to be produced for the senior team and we are expected to win.
"There's a reason why we haven't won this for 37 years and why we haven't progressed as much as we thought we would, because our primary aim is to get players through to Gareth [Southgate].
"Could you imagine a reserve-team manager knocking on the door of a senior manager at a club and saying 'listen boss, I think today you should let me have the best player to win the reserve championship'. That just wouldn't happen.
"The only team that needs to win is the senior team. Everywhere else, winning is part of it, drawing is part of it and having adversity is part of it.
"The reason I say that it is the utterly impossible job is because new players come in, younger players come in and the wheel starts again.
"My job isn't to say to Gareth we should have Jude, Phil or Mason, it is about the senior team and it always will be.
"If someone is doing this job and hiding players and not allowing them to go forward then the system is flawed. I don't want to be the whinge bag to defend myself. They are facts but they are what the job is."
With his England U21 contract running out in the summer, a host of names including Frank Lampard, Steve Cooper, Justin Cochrane and Paul Simpson have all been linked with replacing Boothroyd.
However, the current Young Lions boss has dismissed speculation surrounding his job security and says he still has the desire to carry on the job he started when he took over from Southgate in 2016.
He said: "It's a really good job working for really good people and with really good people, so obviously the runners and the riders are going to get going in this situation but as far as I'm concerned there is nothing to get upset about.
"I'm currently in the chair and have enjoyed being in the chair and want to carry on and do what I think has been a successful job. That's it really. I don't get distracted too much, it's more to focus on the team and the staff.
"I've exchanged a couple of texts earlier in the week and I spoke to Gareth a couple of times. I had a good chat with John McDermott as well.
"Are we on the same page? Absolutely. All the way through the pathway, we're on the same page. We have been for the last seven or eight years.
"You shouldn't be working in youth development if you think your job is to win every game and not produce players for the senior team."
Boothroyd confirmed Callum Hudson-Odoi has suffered a shoulder injury and has returned to Chelsea for further assessment.
The 20-year-old played a full 90 minutes in the 1-0 loss to Switzerland but missed out on the matchday squad for the 2-0 defeat to Portugal on Sunday and Boothroyd confirmed the omission was due to an injury he sustained in the build-up to the game.
"Callum is definitely out and he has gone back to his club, Emile Smith Rowe is also very doubtful," Boothroyd said.
"We have a couple of players we are waiting to hear on, we are giving everyone the longest time we can.
"We have one or two bumps and bruises. I'm going to use the squad and I've got some good players who haven't played yet."
Chelsea midfielder Conor Gallagher, on loan at West Brom, is expected to start in Slovenia.