The Yakult Swallows announced today that Shohei Tateyama had surgery to remove loose bodies in his right elbow. He will most likely require about six weeks for a full recovery.
Source: Yakult announcement
[UPDATE 4/21 @ 7:34pm]
It might take Tateyama about three months before he is ready to rejoin the active roster (six weeks for a full recovery plus six weeks of rehab). He has now had five operations on his right elbow.
Source: Sanspo 4/21/2016