A total of €3.09bn was spent in the summer transfer window of 2021. The past three months have witnessed some of the most expensive as well as strangest deals in the sport's history. In the chaotic month of August, the footballing world was left in shock as Cristiano Ronaldo and Lionel Messi switched clubs in the same window.While the Portuguese superstar made a surprise return to Manchester United, Neymar convinced his best mate Messi to join PSG on a free transfer. With such high-profile signings on the cards, top European sides really brought their A-game to the market this season.Highest spending clubs of the 2021 transfer windowWith three preeminent transfers and one Jack Grealish, both Manchester clubs were the source of most of the cash flow involved. But to everyone's surprise, it was Arsenal who managed to out-spend every single club in this transfer window. The Gunners forked out a massive €165m for the likes of Ben White, Aaron Ramsdale, Takehiro Tomiyasu, Albert Lokonga, Nuno Tavares, and Martin Ødegaard.✅ Lionel Messi 🇦🇷✅ Sergio Ramos 🇪🇦✅ Georginio Wijnaldum 🇳🇱✅ Achraf Hakimi 🇲🇦✅ Gianluigi Donnarumma 🇮🇹✅ Nuno Mendes 🇵🇹 PSG have absolutely smashed the transfer window. One of the greatest we’ll ever see. 🔥 pic.twitter.com/Bb0z298qZr— FutbolBible (@FutbolBible) August 31, 2021Outside of England, RB Leipzig and AS Roma racked up the highest bill, with an expenditure of €107.62m and €97.75m respectively. In the absence of cash-strapped Real Madrid and Barcelona, PSG reigned supreme with some high-quality transfers. While most of the elite clubs were busy splashing insane amounts of cash, Inter managed to earn a colossal profit of €161m. Predictably, Romelu Lukaku's €115m departure was the major reason behind this vast turnover.Contrary to common beliefs, not every big club spent profusely in this window. In fact, there are multiple sides with a notable stature who ended up expending absolutely nothing on transfers. Here, we take a look at 5 significant clubs with no transfer expenditures this summer:#5 Newell's Old BoysLionel Messi paying tribute to Diego Maradona in a Newell shirtMost notably known for being the first club in Lionel Messi's career, Newell's Old Boys have always been a special club for Argentinian talents. Aside from La Pulga, Newell have had several other distinctive alumni. Mauricio Pochettino, Walter Samuel, Ever Banega and Gabriel Batistuta all represented this esteemed club at various youth levels.👕 Messi with a shirt with an image of him dedicating a goal to Diego Maradona by wearing a Maradona Newell's Old Boys shirt from the 1993/94 season [ole] pic.twitter.com/THLT6jngs7— FCBarcelonaFl (@FCBarcelonaFl) July 15, 2021With such a rich history in youth development, the Primera División mainstays have always spent minimal money on transfers. This summer turned out to be no different, as Newell only partook in five incoming transfers. While four of them are loan moves, Gabriel Compagnucci's free signing from Tigre is the only permanent deal sanctioned by the club.This means that the total expenditure carried by Newell amounts to absolutely nothing. In a balancing act, the club did not recoup a single dime from the departures of nine players, nullifying the concept of net-spend. However, with an eighth-place finish last season, manager Fernando Gamboa will wonder whether the Argentine giants were better off splashing some cash after all.#4 HoffenheimTSG Hoffenheim have had disappointing recent seasonsHoffenheim have long been the go-to destination for serious loanees for a long while now, acting as a temporary haven for multiple players. Serge Gnabry, Reiss Nelson and, most recently, Ryan Sessegnon have all played for Die Kraichgauer on a temporary basis.The German club has forked out sumptuous amounts of money from time to time, spending close to €55m in 2019. Nevertheless, Hoffenheim chose to rely on free transfers and a successive loan deal for Bayern Munich prodigy Chris Richards to prepare for the 2021-22 season. Sebastian Rudy swapped Veltins Arena for Rhein-Neckar-Arena to stay in the German top-flight.USMNT’s Chris Richards has returned to Hoffenheim on loan from Bayern for one season, after spending 2020-21 with the club.Bayern announce that the 21-year-old’s contract has also been extended until 2025 ✍️ pic.twitter.com/c2fFZrtR1f— B/R Football (@brfootball) August 31, 2021Having finished as high as third in the 2017-18 season, Hoffenheim have experienced a significant dip in form following Julian Nagelsmann's departure. While the young manager continues to progress in his flourishing career, his former team have been reduced to mid-table regulars. With minimal transfer business during this window, they are well on track to replicate an underwhelming 2020-21 season that saw them slump down to 11th.Also read: 5 biggest transfer downgrades of 2021