Cologne - While the Bundesliga's many stars continue to build up their fitness levels ahead of the new season, clubs up and down the country are working tirelessly behind the scenes to strengthen their playing staff in time for the big kick-off in August.

Over the next few weeks, bundesliga.com will be taking a closer look at each of the 18 top-flight clubs' summer transfer dealings so far. Next in line are SV Werder Bremen...

How they fared in 2014/15...

Bremen fans will be unlikely to forget 2014/15 in a hurry. Rock bottom of the league after nine games, the club parted company with head coach Robin Dutt and appointed Grün-Weiß legend Viktor Skripnik in his stead. What followed was nothing short of remarkable as the Ukrainian led Bremen, powered by the goals of Argentinian forward Franco Di Santo, not only away from the relegation zone but ever closer to the European places. While their continental dream ended with defeat in Dortmund on the final day, optimism had long since been restored at the Weser Stadion.

Ins...

Anthony Ujah (r.) (1. FC Köln)

  • Powerful Nigerian international forward, 24.
  • Registered ten goals in 32 games at 1. FC Köln last campaign.

What he offers: Tireless running, cool finishing and an ability to bring others into play.

Ulisses Garcia (Grasshopper Club Zürich)

  • Hugely promising 19-year-old Swiss left-back.
  • The six-time U-19 international made his UEFA Europa League debut in 2014/15.

What he offers: Energy on the left side, defensive nous beyond his years and massive potential for improvement.

Felix Wiedwald (Eintracht Frankfurt)

  • One of the numerous talented goalkeepers off the Bundesliga production line, 25.
  • Put in an impressive display against Borussia Dortmund in his side's 2-0 win on Matchday 10 last season.

What he offers: Confident shot-stopping abilities, command of his area and a willingness to come off his line.

Outs...

Davie Selke (r.) (RB Leipzig)

  • Promising 20-year-old German striker with Czech and Ethiopian roots.
  • The top scorer at the 2014 UEFA European U19 Championship netted nine goals last season.

Sebastian Prödl (Watford FC)

  • Experienced Austrian campaigner, 28
  • The centre-half, who had been at Bremen since 2008, appeared in three different positions in 2014/15

Nils Petersen (SC Freiburg)

  • Two-footed former Bayern striker, 26.
  • Scored nine goals in 12 games while on loan at Freiburg in 2015.

To-do list...

Having conceded the joint-most goals in 2014/15, 65, top of coach Skripnik's (l.) shopping list for the remainder of the summer will be at least two new defenders. While the signing of left-back Garcia is a step in the right direction, competition for Theodor Gebre Selassie on the other side would be welcomed, while a centre-back to partner Jannik Vestergaard is a necessity. With Zlatko Junuzovic and Fin Bartels, die Grün-Weißen are well stocked in attacking midfield, although a more defensive mind to go alongside Felix Kroos and a winger to supply Ujah and Di Santo up top would also be beneficial.

Editor’s note: Not all summer transfers will be discussed here. The players featured in this article made at least ten league appearances for their respective clubs last season, chipped in with numerous goals and assists or made other significant contributions to their team. For an overview of the 2015/16 summer transfers, click here.