Chelsea recorded a loss of £96.6 million ($128m) for the 2018-19 season, the club announced on Tuesday.
The Blues had posted profits in the previous two years, but a club statement reported the loss was due to player signings, a lack of Champions League football and the dismissal of Antonio Conte and his coaching staff in July 2018.
Conte led Chelsea to a fifth-placed finish in 2017-18, meaning they missed out on Europe's elite club competition in the following campaign.
However, with the arrival of Maurizio Sarri, along with the signings of Kepa Arrizabalaga, Jorginho and Mateo Kovacic, Chelsea then finished third and won the Europa League.
Christian Pulisic's arrival was also included in the results, with the American international signing from Borussia Dortmund in January 2019 and then being sent back on loan to the German club for the remainder of the 2018-19 season.
The club's revenue improved to £446.7m ($592.4m) for the year ended June 30, 2019, and, despite the losses, the statement said they "continue to comply with UEFA's break-even criteria under the Financial Fair Play (FFP) regulations".
Chairman Bruce Buck said: "Consistent revenue growth and careful financial management over recent seasons has allowed the club to make significant levels of investment in the playing staff while maintaining compliance with Financial Fair Play regulations.
"This has contributed to another Europa League victory at the end of the 2018-19 season and a return to the highest level of European competition.
"This solid commercial foundation, allied to a young and exciting team now led by Frank Lampard, means that the club is well-placed to sustain its pursuit of success both on and off the pitch, as well as maintain its financial stability over the coming years."
Chelsea served a transfer ban ahead of the 2019-20 season after FIFA found the club to have breached regulations relating to the international transfer and registration of players aged under 18.
However, the two-window suspension was cut in half in time for Chelsea to make signings in the upcoming January market.
The Blues are currently in fourth place in the Premier League and will take on Brighton in a New Year's Day clash on Wednesday.