Can Northern Ireland halt the German juggernaut? Will Denmark find form before it's too late? And why the result is all that matters for Slovenia against England.
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No time like present for Denmark
Denmark have not missed out on three successive major tournaments for over three decades, but lose here and they could find themselves four points adrift of the top trio in Group E already. Robert Lewandowski was simply too good on Saturday, even if the Danes did cause a few nerves in the Poland camp by pulling it back to 3-2. And it doesn't get much easier on Tuesday, with Montenegro fresh off the back of their biggest ever home win. They are not the same force away, but even at this early stage Denmark cannot afford to slip up.
Denmark v Montenegro, 20:45CEST
No illusions for Northern Ireland
Less than four months after their 1-0 loss to Germany at UEFA EURO 2016, Northern Ireland tackle the world champions once again – with manager Michael O'Neill hoping their Parc des Princes meeting will come in handy. "That's a big thing in our favour," he says. "There will be no surprise element." Set to make "as many as five or six changes" from the side that beat San Marino 4-0 on Saturday, he is braced for a daunting challenge. "If you look at their first two games, they're reacting, possibly, to not having won in France. We have to be ready for that backlash."
Germany v Northern Ireland, 20:45CEST
Slovenia happy to win ugly
We're only three rounds into qualifying, but Jan Oblak reckons Slovenia's meeting with England is already "must-win" for the hosts. An opening draw with Lithuania means Srečko Katanec's side began on the back foot and, having seen at first-hand how England ran away with their UEFA EURO 2016 section, they know this could be their best chance. "We need to make them uncomfortable," says the Atlético keeper. "I don't expect a thing of beauty." Slovenia certainly came close when the sides met in EURO qualifying, Wayne Rooney hitting a late winner.
Slovenia v England, 20:45CEST