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, starting with the Bundesliga's 54th all-time member FC Ingolstadt 04...

How they fared in 2014/15...

Ingolstadt romped to a maiden Bundesliga 2 title in 2014/15, remaining top of the table from Matchday 8 onwards. Die Schanzer's success was built upon a solid defensive unit, the engine room of Roger and Alfredo Morales combined with the artistry of Pascal Groß in midfield and a versatile attacking trio who shared out the goals. Australian international Mathew Leckie struck on seven occasions, while Stefan Lex and Lukas Hinterseer both netted nine times. As Marvin Matip summed up so eloquently after Ralph Hasenhüttl's side sealed the league title on Matchday 33: "We're in the Bundesliga - it's going to be amazing!"

Ins...

Elias Kachunga (r.) (SC Paderborn 07)

  • Cologne-born 22-year-old striker
  • Netted six goals in his debut Bundesliga season with SC Paderborn 07 in 2014/15

What he offers: Strong work ethic, pace and composure in front of goal

Romain Bregerie (SV Darmstadt 98)

  • 28-year-old French centre-back who formed part of the Bundesliga 2's best defence last season
  • Offers a genuine threat from set-pieces: Bregerie scored six goals for Darmstadt in 2014/15

What he offers: Strength in the tackle, dominance in the air and an impressive record from the penalty spot

Markus Suttner (FK Austria Wien)

  • Austrian left-back with 14 international caps to his name, 28
  • Made 31 appearances and picked up three assists in 2014/15 as Austria Wien finished seventh

What he offers: High fitness levels, excellent crossing ability and composure in possession

Outs...

Karl-Heinz Lappe (r.) (FC Bayern München reserves)

  • 27-year-old striker who led the line impressively on 14 occasions in 2014/15
  • Scored one goal, on Matchday 2 against Darmstadt

Andre Weis (FSV Frankfurt)

  • Former Stuttgart goalkeeper who had been at the club since 2013
  • The 25-year-old impressed when called upon last season

Andre Mijatovic (Retired)

  • 35-year-old Croatian centre-back who is a veteran of 64 Bundesliga appearances and 170 in the second tier
  • Turned out 11 times for FCI last season, netting once

To-do list...

While Kachunga fills the need for an out-and-out striker, Bregerie offers a direct replacement for Mijatovic, Suttner will provide cover at full-back and Norwegian international Orjan Nyland will compete with Ramazan Özcan for the number one spot, Ingolstadt coach Ralph Hasenhüttl is unlikely to view his transfer business as done and dusted just yet. Die Schanzer's squad still looks a little light, with youngsters Robert Bauer and Max Christiansen the only real back-up in central midfield, where an experienced campaigner could come in handy. Another reliable goalscorer wouldn't go amiss, either.

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.