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 mid 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 up in the series are the Billy-Goats, 1. FC Köln…

How they fared in 2014/15...

You won't hear the Köln fans complaining after the Billy Goats comfortably negotiated their first season back in Germany's top flight after winning the Bundesliga 2 title in 2013/14. A solid defensive foundation ensured they became the only promoted side to go an entire season without spending a single day in the relegation zone: to reinforce the point, only the top four - FC Bayern, VfL Wolfsburg, Borussia Mönchengladbach and Bayer 04 Leverkusen - conceded fewer goals all campaign.

Ins...

Milos Jojic (r.) (Borussia Dortmund)

  • Five-time Serbian international midfielder
  • Scored with his first touch on his Bundesliga debut in Dortmund's 4-0 win over Eintracht Frankfurt on 15 February 2014.

What he offers: No-nonsense approach in the engine room with an eye for goal.

Leonardo Bittencourt (Hannover 96)

  • Has chalked up six goals and nine assists in 62 Bundesliga outings to date
  • Brazilian father, Franklin, played for Energie Cottbus (1998-2003)

What he offers: Can play on either flank, loves to take players on and gets balls into the box

Anthony Modeste (TSG 1899 Hoffenheim)

  • Netted 19 times in 55 Bundesliga appearances for Hoffenheim
  • Has already played for six different clubs since turning professional

What he offers: A classic centre-forward with a nose for goal

Outs...

Anthony Ujah (r.) (SV Werder Bremen)

  • Köln's top scorer for 2014/15 with ten strikes in 32 Bundesliga appearances
  • Famously celebrated a goal with Köln mascot Hennes VIII in last season's 4-2 win over Eintracht Frankfurt

Kevin Wimmer (Tottenham Hotspur FC)

  • Part of a Köln back four that conceded just 20 goals in 34 Bundesliga 2 games in 2013/14
  • Put his pace and tackling ability to good use again in 2014/15, starting all but two of the Billy Goats' top-flight assignments

Adam Matuschyk (Eintracht Braunschweig)

  • 21-time Poland international midfielder
  • Has turned out 110 times in Germany's top two divisions for Köln and Fortuna Düsseldorf

To-do list...

Peter Stöger has lost two of his most influential players in Wimmer and Ujah, but he's compensated wisely in the transfer market whilst adding some much-needed beef and creativity to the midfield. That said, another striker capable of posting double figures wouldn't go amiss, seeing how Köln scored the fewest number of goals (34) of all teams outside the bottom three last term.

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.