Tetsuya Matsumoto held a press conference on October 6 and announced that this would be his last year. He told reporters that he decided to retire because he was unable to make the active roster this year. He talked things over with his family and made the decision. His last official game will be the Farm Championship on October 7.
Matsumoto began his career when the Yomiuri Giants selected him in the third round of the Ikusei draft in 2006. He quickly made the seventy-man roster before the start of the 2007 regular season, but did not play in any Ichi-gun games until the following year on May 28, 2008. He played his first full season in 2009 and won the Rookie of the Year award. He made the All-Star team in 2010 and helped the Giants win two Nippon Series championships (2009 and 2012).
[UPDATE 10/7 @ 10:39pm]
Matsumoto got some playing time during the Farm Championship game today. He entered the game as a pinch-hitter in the bottom of the eighth and grounded out to third. He remained in the game and played center in the top of the ninth. Teammates tossed him into the air eight times after the game.
Source: Nikkan Sports 10/7/2017
[UPDATE 11/24 @ 3:45pm]
The Giants held a retirement ceremony for Matsumoto during Fan Festa on November 23.
Source: Yomiuri 11/24/2017