The NFL Players Association headquarters in Washington, D.C., suffered limited damage by a fire Tuesday morning, executive director DeMaurice Smith said.
The fire apparently began in Smith's office at approximately 5 a.m. and nobody was injured, he said.
"Most of the damage was caused by the internal sprinkler system," Smith said. "We don't know a lot more, other than there is an investigation that is now under way."
There is no initial finding of arson but the NFLPA has given access to its security video system to investigators, Smith said.
Smith had just returned early Tuesday morning on a red-eye flight from San Francisco during his trek to meet with players from all 32 NFL teams.
Chris Mortensen is a senior NFL analyst for ESPN.