Klopp's new core at Liverpool

Borussia Dortmund mainstay Roman Weidenfeller warned his side to be on alert for Thursday's second leg at Anfield, saying former coach Jürgen Klopp would seek to use his insider knowledge to turn the tie against the Bundesliga outfit.

"Klopp knows Borussia inside and out, the team too. He's very familiar with individual players' strengths. So he will try to keep our players in check tactically, or shut them out of the game altogether," Weidenfeller told Sport 1. "He'll also try to inspire his players to battle their way into contention."

Thomas Tuchel and Dortmund, you could argue, are at something of a disadvantage - knowing less about the individual dangers posed by Klopp's new crew.

Klopp inherited a strong squad from his predecessor Brendan Rodgers. A happy mixture of talented youngsters in need of refinement and experienced warhorses capable of meeting the coach's physical demands for high-octane football. We've selected six key figures, from those available to play in Thursday's second leg.

Mamadou Sakho - the ungainly rock

Sakho and his partner in central defense, Dejan Lovren, have taken a lot of stick this season. Former Dortmund man Steffen Freund, now busy in Tottenham's backroom, highlighted the pair this week as Liverpool's main weakness. The very way Sakho moves - he comes across as rather a clumsy colossus at times - might help explain the criticism.

But in truth, Sakho and Lovren have made progress under Klopp, with the French international in particular turning into an imposing figure at the heart of the defense. Besides a string of strong showings in the Premiership of late, this was perhaps most visible at the Signal Iduna Park in the first leg. The left-footer was imperious in the air, blocked several key shots, and kept Pierre-Emerick Aubameyang confined to his hip pocket.

Emre Can - the destroyer-in-training

Klopp's German international - Liverpool's first since Dietmar Hamann - has grown into a crucial and now relatively consistent role in holding midfield. At first, as at Bayern Munich and Leverkusen before that, Can's versatility left him playing all over the park for Rodgers' Liverpool: at full back, on the wing, in a back three, in central midfield.

Now, Can regularly lines up in front of the back four. And the 22-year-old has bulked up for the role, throwing his weight about with real abandon as Klopp's midfield mischief-maker. The last Europa League round against Manchester United, in which Can physically overpowered the big Belgian Marouane Fellaini time and again, provided prime examples of Can's hard-man Premiership persona.

James Milner - the upmarket Kevin Grosskreutz

Any number of Liverpool's hard-working England internationals deserved a mention in this list. Captain Jordan Henderson's first-leg injury ruled him out of contention. Adam Lallana - another fan of Klopp's motivational techniques - has enjoyed a renaissance in attacking midfield. Full back Nathaniel Clyne is a pacy weapon down the right or left.

However, it's James Milner who made our cut. The Leeds lad is somewhat similar to BVB's former cult favorite Kevin Grosskreutz in a number of ways. Rarely a match-winner in his own right, Milner can do almost any job demanded of him and boasts a work ethic to match Klopp's passion for pressing. Consistent, with years of title-challenging Premiership experience, he's a fine crosser and corner-taker, to boot.

Philippe Coutinho - the hit-and-miss magician

On his day, Coutinho is simply Liverpool's most dangerous player. The Brazilian number 10 is good for 10 to 15 spectactular goals every season, although he also has an unfortunate habit of going missing more often than a playmaker should. The 23-year-old has the full package of skills, quick and slippery on the ball, a solid passer, with a hammer of a right boot. Julian Weigl and Ilkay Gündogan will need to keep Coutinho quiet - not least as he has a habit of saving his screamers for the big stage. In his Liverpool career, he's netted five against Manchester City, two against Chelsea and Tottenham, and one against Arsenal, Everton and Manchester United.

Roberto Firmino - the all-purpose attacker

After a tough start to the season, following his big-money move from Hoffenheim, Firmino has established himself as an important piece of Klopp's attacking puzzle. Effective in games both leading the line and playing off a traditional striker (more on them in a moment), the Brazilian has fostered quite a partnership with his countryman Coutinho and midfield workhorse Lucas Leiva - another player revitalized since Liverpool's change of management.

Divock Origi - to Sturridge and Benteke's dismay

Let's conclude with the up-and-comer in the squad. Belgian international forward Divock Origi looked like one for the future - or possibly one for the wing - when Liverpool brought him in last season. With injury-prone England international Daniel Sturridge established, and fellow Belgian Christian Benteke joining from Aston Villa, Klopp seemed to have an abundance of options for the lone striker he prefers to field.

Recently, however, 20-year-old Origi has begun to lay claim to the number nine spot himself. Klopp chose him on tactical grounds in the first leg against BVB, eyeing the mixture of pace and power afforded by the youngster. Origi rewarded the gaffer with Liverpool's crucial away goal. At the weekend, he came on at half-time and scored twice as Liverpool bested Stoke City 4-1.

"He's always believed in me and he believes in the group also," Origi said of his latest boss. "The fact that I'm on the pitch gives me confidence and I just try to play my game and enjoy it."

Like Milner and Grosskreutz, Origi might well remind Klopp of another pacy winger who's good in the air and on the deck, reinvented with great success as an out-and-out striker. Pierre-Emerick Aubameyang and Origi are cut from remarkably similar cloth.