The outfielder underwent a successful surgery to fix a complication of a cavernous malformation in his brain on Friday, according to the Red Sox.
The surgery was performed by Dr. Robert Spetzler at the Barrow Neurological Institute at St. Joseph's Hospital and Medical Center in Phoenix.
This was the second such surgery for the minor leaguer, who first underwent the procedure in 2010 after the malformation was initially detected.
Westmoreland is a former highly-regarded prospect who has not appeared in a minor league game since playing for the short-season Single-A Lowell Spinners in 2009.