Chelsea have recorded a loss of £96.6 million for the year ending June 30, according to the Premier League club's latest financial results released on Tuesday.
After two profitable years, Chelsea insisted they are still compliant with UEFA's Financial Fair Play regulations.
The club cited a lack of Champions League football, costs associated with changing manager and a record outlay on players Kepa Arrizabalaga, Christian Pulisic, Mateo Kovacic and Jorginho for the loss.
Turnover grew slightly to £446.7 million.
"Consistent revenue growth and careful financial management over recent seasons has allowed the club to make significant levels of investment in the playing staff whilst maintaining compliance with UEFA Financial Fair Play regulations," Chelsea chairman Bruce Buck said on chelseafc.com.
"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 made a £62 million profit in the previous year.
The London club is fourth in the Premier League, 20 points behind leader Liverpool, and plays at Brighton on Wednesday.