Tomoya Mori left a game against WBC Cuba on March 5 early because he took a pitch off his left elbow during his at bat in the fourth inning. He left the field for treatment and did not return. He told reporters after the game that he was okay.
Mori was examined at a hospital in Osaka today and a fracture was discovered in his left olecranon. He is scheduled to return to Tokyo for additional tests with the team doctor.
[UPDATE 3/29 @ 11:29pm]
Surgery was a possibility, but Mori and the Lions opted for non-surgical treatment. He is slated to begin a rehab program in April. He will most likely require more than two months for a full recovery.
Source: Daily Sports 3/29/2017
[UPDATE 5/6 @ 5:41pm]
Mori tossed batting practice at Seibu 2 Stadium earlier today. He spent about thirty minutes throwing over 150 pitches to Yuji Kaneko and Aito Takeda. Based on his current progress, he might not be ready to return to the active roster until some time after Inter-league play.
Source: Tokyo Sports 5/6/2017
[UPDATE 6/14 @ 2:39pm]
Mori is making slow progress. An examination revealed that the fracture in his left elbow was still not fully healed. There is also a difference in size of two to three centimeters between his arms. He might not be ready to play in rehab games until some time in late-August.
One big reason for the slow progress might have something to do with Mori’s decision to go with non-surgical treatment.
Source: Tokyo Sports 6/14/2017