As the clock struck 6pm on Friday, all trading on the summer transfer window was officially over.

The 18 Bundesliga sides have spent the summer wheeling and dealing, finding the players they believe can deliver them success this season. Among the many movers and shakers, have picked out five to keep an eye on…

Paco Alcacer

Age: 25
Nationality: Spanish
Position: Striker
Arrives from: Barcelona (loan)

What to look out for:

Could the Spain international be the final piece of the puzzle for Dortmund? Following the departures of Pierre-Emerick Aubameyang and Michy Batshuayi, BVB were at risk of going into this without a recognised first-team striker. Alcacer is that, and he guarantees goals.

Paco Alcacer has joined Dortmund from fellow Champions League participants Barcelona. © gettyimages / LLUIS GENE/AFP

Despite finding playing time at Barcelona limited, the striker still chipped in with an impressive 15 goals and eight assists in 50 competitive appearances. His record at previous club Valencia is just as potent with 43 goals and 17 assists in 124 outings, showing the striker has an eye both for goal and a teammate. Being served by the superb attacking talents of Marco Reus, Christian Pulisic and Mario Götze, Alcacer could finish his season-long loan with a bucket-load of goals and perhaps push Dortmund on from their fourth-place finish last year.

Kevin Trapp

Age: 28
Nationality: German
Position: Goalkeeper
Arrives from: Paris Saint-Germain (loan)

What to look out for:

You don’t become Germany’s third-choice keeper for nothing. Trapp may be behind Manuel Neuer and Marc-Andre ter Stegen for Joachim Löw, but he has seen off competition from former Bayer Leverkusen No.1 Bernd Leno, VfB Stuttgart’s 2014 World Cup winner Ron-Robert Zieler and others to remain an integral part of the national team set-up.

Trapp is back for a second spell with Eintracht Frankfurt, after a success-filled spell in France. © gettyimages

With the experience of 12 Champions League appearances and nine Europa League outings, and an unbeaten record in PSG's successful Coupe de France campaign last season, he will now be keen to get a regular game again for the Eagles – a club he knows all too well from 96 previous appearances during his first spell with them – and help prop up their challenge on three fronts this term.

Axel Witsel

Age: 29
Nationality: Belgian
Position: Midfielder
Arrives from: Tianjin Quanjian

What to look out for:

After spells in his native Belgium, Portugal, Russia and most recently China, Witsel has taken to German football like a duck to water. He scored a vital injury-time equaliser on his debut in the DFB Cup, and then netted again in his maiden Bundesliga outing against RB Leipzig. Even just two games into his Dortmund career he is already proving how important he could be to Lucien Favre’s side.

Witsel has made an immediate impression as a Borussia Dortmund player. © imago

The fact the 96-time Belgium international has already started chipping in with goals is simply a bonus. Primarily a defensive midfielder, Witsel was signed to add that necessary grit and experience at the centre of Borussia’s game. The bar has been set high with just two games to his name, let’s see if he can keep it up.

Leon Goretzka

Age: 23
Nationality: German
Position: Midfielder
Arrives from: Schalke

What to look out for:

Another product of Schalke's famed Knappenschmiede production line, Goretzka already has 117 Bundesliga appearances to his name, yet he is still only 23. Capped 15 times by Germany, he has six goals for his country and is considered by many to be the player Bayern had been lacking in their midfield since losing the likes of Bastian Schweinsteiger and Toni Kroos.

WATCH: Bayern looking to the future with Goretzka

Those two are, indeed, role models for the dynamic, box-to-box midfielder who likes nothing more than to have the ball at his feet, progressing from deep and creating opportunities or, if needs be, showing his own shooting ability to deadly effect.

Davy Klaassen

Age: 25
Nationality: Danish
Position: Attacking midfielder
Arrives from: Everton

What to look out for:

Klaassen really caught the eye in the 2013/14 campaign when he scored 12 goals and provided four assists across all competitions for Ajax on their way to the Dutch league title. He proved he was no one-hit wonder the following season with eight more goals and a further 12 assists and such was his influence on the team by that point that he was made Ajax captain at start of 2015/16 and he repaid the club's faith in him with another barnstorming year that ended with him being voted Dutch Player of the Year by his fellow professionals in 2016.

WATCH: Klaasen wants European football with Bremen

A move to Everton followed, but he struggled to make his mark in the Premier League and he now arrives in Germany with the burning desire to prove the critics wrong, and Bremen fans are licking their lips in anticipation of the Ajax version of defence-destroying Davy Klaasen.

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