After 21 at-bats, Matsui is hitting just .143 with three RBIs as of Monday.
Rays manager Joe Maddon said there is no timetable for Matsui to possibly join the Major League club but did say that the would consider brining him up when he's both ready and needed.
"I've heard he's doing fine," Maddon said. "I was talking to Andrew [Friedman] about it, we're checking up on it more closely. We're trying to get more opinion on it right now, but I haven't heard anything bad."
Matsui is a career .285 hitter in nine Major League seasons with the Yankees, Angels and A's. He has 173 career home runs and 753 RBIs. Last season with Oakland, he hit .251 with 12 home runs and 72 RBIs.