According to a report by Nikkan Sports, Yuichi Matsumoto is planning to retire after the seaon. He has already spoken to members of the organization and an announcement will most likely be made before the Nippon Series. Matsumoto is quoted as saying, "I've given it everything I got. I really appreciate the team keeping me around for seventeen years, even though I never managed to win an everyday job."
Source: Nikkan Sports 10/18/2015
[UPDATE 1/3/2016 @ 1:44am]
Matsumoto accepted a job as a Ni-gun hitting coach in the Swallows' organization.
Source: Daily Sports 1/2/2015