Germany's defence will be put to the test in their opening Euro 2016 group match against Ukraine in Lille on Sunday with major questions still to be answered about the world champions' new-look rearguard.
Coach Joachim Loew's team will be without key central defender Mats Hummels, still recovering from a muscle injury, as they kick off their Group C campaign.
Hummels' replacement Antonio Ruediger was ruled out with torn cruciate knee ligaments this week.
Holding midfielder and captain Bastian Schweinsteiger, still working on his comeback from injury, is also absent, further complicating Loew's defensive conundrum.
Benedikt Hoewedes and Jerome Boateng are the two likely central defenders but both had a long injury break late in the season and are in desperate need of match practice.
Jonathan Tah, the 20-year-old who was only called up this week following Ruediger's injury, is expected to be on the bench.
Toni Kroos, who will shoulder the biggest responsibility of connecting Germany's defensive and attacking game, is brimming with confidence following his Champions League win with Real Madrid.
Assistant coach Thomas Schneider sounded confident on Friday that the team would quickly find their cohesion at the back.
"In the last few matches we thought a lot about our defensive operation and we came up with a few things, including for defensive set pieces," he said.
"We have worked on that in training and everyone knows their job."
Ukraine, while outsiders, are certain to test the Germans' new-look defence with quick wingers Andriy Yarmolenko and Yevhen Konoplyanka capable of inflicting severe damage.
It will be up to Loew's full backs to neutralise that threat but they must also break down a steely Ukraine defence.
The Germans, eyeing their fourth Euro triumph but first since 1996, have never lost an opening match at the European Championship and are aware a slip-up could prove costly.
"The first game is extremely important and it will determine our run in this tournament," attacking midfielder Julian Draxler said.
Ukraine managed to keep six clean sheets in 10 qualifiers with coach Mykhailo Fomenko having taken over after the co-hosts' disappointing Euro 2012 campaign.
They then came out on top against Slovenia in a playoff last year, with the 67-year-old having moulded them into an efficient unit.
Croatia out to banish memories of Euro 2008 failure
Croatia will seek to erase the bitter memories of their Euro 2008 failure against Turkey, described by key players as their most painful defeat ever, when they meet in this year's Group D opener in Paris.
The Croatians had one foot in the last four eight years ago, after taking a 1-0 lead in the final minute of extra time in an epic quarter-final clash in Vienna, only to concede with the last kick of the game before they lost in a penalty shootout.
Croatia have not reached the knockout stages of a major tournament since and defender Vedran Corluka, a survivor from the 2008 side, said navigating a tough group was more important than getting revenge.
"The bitter feeling of that loss can only be compensated by winning the European Championship," the 30-year-old centre back told a news conference in the team's Deauville base camp in northern France on Friday.
"It's the distant past and not really in the focus of our preparations but we can push it further back in our minds and, more importantly, make the right start if we beat them at the Parc des Princes."
Influential playmaker Luka Modric, who missed the opening penalty for Croatia in the 2008 shootout, added: "I cried like a baby that night, it was the biggest setback of my career."
Turkey have failed to qualify for a major tournament since their impressive Euro 2008 campaign, having been knocked out in the 2012 European Championship playoffs after a 3-0 aggregate defeat by Croatia.
Their coach Fatih Terim, who steered his battling team to the semi-finals eight years ago, acknowledged that beating the Croatians was imperative ahead of matches with holders Spain and Czech Republic.
"Winning this game would pave the way for a last-16 berth," Terim was quoted as saying by Turkish media.
"I believe that if we work hard, we can advance."
Terim is likely to field the side which beat Slovenia 1-0 in a friendly on Sunday, with scorer Burak Yilmaz set to the lead the line in front of the versatile Arda Turan and gifted 22-year-old playmaker Hakan Calhanoglu.
Croatia's attacking midfielder Ivan Rakitic singled out his Barcelona team mate Arda as the biggest threat.
"He is a truly outstanding player and pulls all the strings for Turkey, therefore we have to close him down in order to keep a clean sheet."
Poland face test of patience against Northen Ireland
Poland face a test of patience and their nerves when they open their Euro 2016 campaign against a Northern Ireland side who want to make themselves "horrible" to play against.
Sunday's group C match will pit one of the most attack-minded of the 24 teams at Euro 2016 against a team who have made no bones about their intentions.
Spearheaded by the attacking duo of Robert Lewandowski and Arkadiusz Milik, Poland were the highest-scoring team in the qualifying competition with 33 goals, 13 of them coming from Bayern Munich's Lewandowski.
Coach Adam Nawalka has turned them from a counter-attacking side into one that keeps possession and build attacks carefully.
He has also bucked the trend of teams playing with a single, or no, striker, expressly to give Lewandowski more support, a tactic which has worked wonders so far.
The huge expectations back home, however, will put Poland under considerable pressure as they attempt to pass the group stage at the Euros for the first time, and Northern Ireland are just the team to play on their anxiety.
Northern Ireland have limited resources but manager Michael O'Neill clearly knows their place and makes no apologies for a playing style which is likely to prove a test of endurance for spectators as well as the opposition.
“We are going to have to be horrible to play against,” he said recently. “We are going to be really good without the ball, run further than any other team, drill all the statistics back in their face. Sixty-five per cent possession? We don’t expect to have that.”
The Euro debutants' squad includes 13 players based with lower-tier sides in England, five from the English Premier League, four from the Scottish Premier League and one from Australia's A-League. None of them play in continental Europe.
Despite this, they conceded only eight goals in qualifying and are unbeaten in their last 12 matches, a run stretching back to March last year and the longest in the team's history.
"It's a fantastic achievement to be out here but having achieved that we want to leave our mark on the tournament," said O'Neill. "There is a sense of excitement for all of us. This is a new experience for myself (and) for all of the players."