Alex Rodriguez's legal team began cross-examination of Biogenesis founder Anthony Bosch on Thursday, according to a source, as the appeal of the Yankees third baseman's 211-game suspension continued at Major League Baseball's headquarters in Manhattan.

Bosch, who ran the defunct anti-aging clinic in Miami that was the center of MLB's investigation into performance-enhancing drugs, is considered the league's star witness against Rodriguez. Bosch spent nearly three days giving testimony

Rodriguez, who was suspended on Aug. 5 but allowed to play during the appeal process, has appeared at each of the first four sessions of the hearing, which began Monday. He refused to answer any questions as he left Thursday's session surrounded by a sea of autograph-seekers.

The source said it is uncertain whether Rodriguez will testify during the hearing. Rodriguez last week refused to say whether he will testify.

A person familiar with the arbitration process said Rodriguez cannot be compelled to testify and that the arbitrator will not penalize him for not doing so.

"The job of any fact-finder is to make a judgment," the person said. "It is the obligation of the charging party [MLB] to prove its case. That's going to be the choice of the grievant and his council."

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If Rodriguez does testify, he will open himself to be questioned by MLB's attorneys, unless, the person said, "there is some type of agreement between the parties that limits his testimony."

Washington attorney Stanley Brand said, "I believe it is extremely risky" for Rodriguez to testify. "That testimony would be fully available to the government if it is determined that it was relevant to the commission of federal crimes involving controlled substances."

The first week of Rodriguez's hearing is scheduled to end Friday. No future dates have been announced. Arbitrator Fredric Horowitz will have 25 days from the conclusion of the hearing to uphold, overturn or alter the suspension.