The 32-year old is competing with Matt Davidson, Carlos Sanchez and Jerry Sands for the final spot on the 25-man roster.
Ishikawa was also the beneficiary of Adam LaRoche's surprise retirement. Ishikawa, like LaRoche, is a left-handed hitter who can serve as Jose Abreu's backup at first base.
Ishikawa also brings a bit of versatility as he's played 17 career games in the outfield.
"You're looking at a guy that can play first base, a little bit of outfield and can swing it from the left side," Ventura said. "I think the more looks we really get of him, it's just a better understanding of where he's at, what we need."
• Alex Avila left Saturday's game with lower back tightness and was out of the lineup Sunday and Monday, but Ventura expects Avila back behind the plate Tuesday. Ventura also said Avila hit in the cage Monday.