Michael Weiner, the executive director of the Major League Baseball Players Assn., has been diagnosed with a brain tumor, the MLBPA announced Tuesday.
In a statement, the union said Weiner began treatment on Monday. The treatments are expected to last for about a month, with Weiner expected to report to work daily during that time, according to the statement.
"He looks forward to making a full recovery," the statement read.
Weiner, 50, succeeded Donald Fehr as leader of the players union in 2009 and negotiated a new collective bargaining agreement last year, helping baseball keep labor peace even as strife hit the NFL and NHL.
Weiner is extremely popular within the sport, even among his professional adversaries at the commissioner's office.