Aug 28, 2010 11:09 AM EST

Major League Baseball is investigating Yankees pitcher Ivan Nova and minor league hurler Wilkin De La Rosa for allegedly injecting each other with B-12 shots last season.

At the time, they were teammates in Double-A Trenton.

Though B-12 isn't on the list of baseball's banned substances, only licensed physicians are allowed to inject medication.

Nova made his first major league start Monday against the Blue Jays in Toronto.

Via New York Post