"This morning, after Bud Selig refused to come in and testify about his rationale for the unprecedented and totally baseless punishment he hit me with, the arbitrator selected by MLB and the players' association refused to order Selig to come in and face me. The absurdity and injustice just became too much. I walked out and will not participate any further in this farce."
Rodriguez's legal team remains involved in the proceeding. Rodriguez said he had planned to testify later this week but was warned by the union he could face additional discipline if he did.
In a lengthy interview on WFAN, Rodriguez said he consulted Biogenesis of America head Anthony Bosch for "nutrition and weight loss."
Rodriguez repeatedly denied using performance enhancing drugs during the period in question and said Selig "hates my guts," is "trying to destroy me" and "doesn't have the nerve to come and face me face to face."
Horowitz technically is chairman of a three-man arbitration panel that also includes Manfred and Dave Prouty, the general counsel of the players' union.
"For more than 40 years, Major League Baseball and the players' association have had a contractual grievance process to address disputes between the two parties. This negotiated process has served players and clubs well," the commissioner's office said in a statement. "Despite Mr. Rodriguez being upset with one of the arbitration panel's rulings today, Major League Baseball remains committed to this process and to a fair resolution of the pending dispute."
The players' union said it disagreed with the arbitration decision, but added that it would abide by Horowitz's refusal to make Selig testify.
"The MLBPA believes that every player has the right under our arbitration process to directly confront his accuser," the union said in a statement. "We argued strenuously to the arbitrator in Alex's case that the commissioner should be required to appear and testify. While we respectfully disagree with the arbitrator's ruling, we will abide by it as we continue to vigorously challenge Alex's suspension within the context of this hearing."
Rodriguez was suspended Aug. 5 for alleged violations of the sport's drug agreement and labor contract, and the players' union filed the grievance to overturn the penalty. Under baseball's drug agreement, he was allowed to continue playing while contesting the discipline.
The three-time AL MVP said four years ago he used performance enhancing drugs while with the Texas Rangers from 2001-03, but has denied using them since.
At the time of his suspension, MLB said the penalty was for "use and possession of numerous forms of prohibited performance-enhancing substances, including testosterone and human growth hormone over the course of multiple years" and for "engaging in a course of conduct intended to obstruct and frustrate the office of the commissioner's investigation."
