The New York-listed company lost 6% from its share price last week since reporting the injury-free incident on Thursday.
Foresight told the St Louis Post-Dispatch that the fire was contained to an already-mined section of Deer Run.
The company was also encouraged by lower carbon monoxide readings after it pumped water into the mine throughout the weekend.
“Foresight is waiting for the Mine Safety and Health Administration to determine it is safe to enter the mine before it can estimate the damage,” the newspaper reported.
“The company said it doesn’t anticipate the fire will materially hurt financial results.”
Located near Hillsboro in Illinois, the underground thermal coal mine typically produces about 500,000 short tons per month.