Having led the Bundesliga table for the majority of last season, the wheels came off in dramatic fashion as Dortmund surrendered a nine-point lead after 15 games to ultimately finish second to Bayern Munich by two points.
Such was their failure to sustain their title challenge that question marks were raised over Lucien Favre's side's mental toughness, as well as certain areas for concern in their squad.
The Swiss manager has already set about restructuring his squad this summer, with four players walking through the door as Die Borussen eye their first league title since 2012.
However, where else could they strengthen? Julian Brandt, Thorgan Hazard, Nico Schulz and Mats Hummels are all set to don the yellow and black next season but improvements could still be made as they look to dethrone Bayern from their spot atop the German football pyramid.
Competition for Paco Alcacer
After making his move to Dortmund permanent midway through his season-long loan from Barcelona, Alcacer has shone for Favre's side. The Spaniard netted 12 goals in his first 14 games, with ten of those coming from the bench to set a new Bundesliga record for number of goals scored by a substitute. A further six goals followed after he penned a full-time deal, as he enjoyed an excellent start to life in Germany.
Nevertheless, he has been forced to take the brunt of the workload given he is the only recognised striker at the club with any real experience. Mario Gotze isn't really a striker but has slotted into the role, fitting the mould of how Favre likes to play, yet he doesn't score enough goals to warrant a regular place. Equally, Marco Reus has played up front at times last season, yet he too is wasted when unable to link up with play as efficiently as he does from the number ten role.
Alexander Isak was surprisingly moved on this summer so additional striking options should definitely be somewhere this window. Max Kruse would have posed an interesting option, but the German has since moved to Turkey, while Sebastien Haller of Eintracht Frankfurt would add a physical presence Dortmund are sorely lacking - although he is likely to cost too much.
Beef Up Central Midfield
Thomas Delaney and Axel Witsel formed an excellent partnership throughout last season, complementing each other brilliantly in the heart of midfield. Mahmoud Dahoud is the next in line to take one of the midfield spots in the absence of the pair, but just 14 league outings last season would indicate Favre isn't too keen on the German.
The club have a plethora of wide attacking players at their disposal but in order to balance out the squad there is a definite need to bolster the central midfield roles. If anything, just to ease the burden on Delaney and Witsel for the upcoming campaign, where Dortmund are set to compete in four competitions.
Julian Weigl's future at the club is uncertain, therefore it could leave Favre with just three recognised players for the position. Nadiem Amiri is a name that has been mentioned and could fit the bill if Dortmund were looking for players with Bundesliga experience.
A Replacement for Lukasz Piszczek
With two players already occupying the right-back role, it may seem a strange position to strengthen. However, club stalwart Lukasz Piszczek will head into the coming campaign at the age of 34, and while he can still most certainly do a job for the club, his best days are behind him.
The other option for Favre is the much younger Achraf Hakimi. The Moroccan is about to embark on the second season of his two-year loan from Real Madrid and impressed during his first year in the Bundesliga.
Injuries hampered much of his campaign but when given the chance he has shone down the right-hand side. Making his loan move permanent will definitely be under consideration by the Dortmund hierarchy, especially if he performs to the same level as the previous season.
Cover for Raphael Guerreiro
Unquestionably a fine defender, Guerreiro has made the left back spot his own ever since dropping back into the position having initially been a winger. The Portuguese ace is still only 25-years-old and likely to remain as the club's first choice for a good few seasons.
It doesn't mean adequate cover, or even competition, should be sought after though. Nobody else in the squad is capable of playing left back, with the exception of Hakimi. Dan-Axel Zagadou has filled in the role at times this past season, but the young Frenchman is far more comfortable at centre back.
Favre favours a back four when setting his team up and the role of the full backs is vital when his side are in transition, therefore some extra cover to handle the sheer quantity of matches is something to look at. Ricardo Rodriguez from AC Milan is available and has Bundesliga experience, although it would be difficult to see the Swiss international accept a back-up role.