A league spokesperson tells us, "The XFL quickly captured the hearts and imaginations of millions of people who love football."

"Unfortunately, as a new enterprise, we were not insulated from the harsh economic impacts and uncertainties caused by the COVID-19 crisis."

"Accordingly, we have filed a voluntary petition for relief under Chapter 11 of the U.S. Bankruptcy Code."

"This is a heartbreaking time for many, including our passionate fans, players and staff, and we are thankful to them, our television partners, and the many Americans who rallied to the XFL for the love of football."

Sources tell us ... the COVID-19 pandemic, which essentially shut down the league -- caused the XFL to lose "tens of millions in revenue" since it wiped out regular-season games and playoff games.

We're told ... despite the financial blow, employees were paid full wages up until April 12 as well as any accrued vacation days.

We're also told the XFL will refund ticket holders, and are currently in that process.

As for the filing, we're told the timing was to maximize the return investors.

Among the creditors ... XFL lists head coaches Bob Stoops ($1,083,333.33), Mark Trestman ($777,777.78), Jonathan Hayes ($633,333.33), Winston Moss ($583,333.33) and others.