Recently, according to Mike Puma of the New York Post, A-Rod underwent an “experimental” knee treatment in Europe:

The innovative procedure was performed on Rodriguez — with the Yankees’ blessing — within the last month, according to one source. The Yankees first cleared the procedure with the commissioner’s office to avoid the appearance that Rodriguez might be receiving impermissible treatment.

The article further indicates that A-Rod did this after getting advice from the Los Angeles Lakers‘ Kobe Bryant, who had a similar treatment called “Orthokine” done in Germany:

Orthokine involves taking blood from the patient’s arm and spinning it in a centrifuge, a machine used in laboratories to spin objects around a fixed axis. The serum is then injected into the affected area — in this case, Rodriguez’s knee.

Read more at SB Nation