Two players to be named later or cash considerations are headed back to Tampa Bay. To make room on the 40-man roster the Cubs designated catcher Josh Phegley for assignment.
The Cubs get a right-handed hitter who mashes lefties in Martinez. Chicago ranks 27th in batting average against lefties this year and was 30th last season. Martinez is a career .319 hitter against left-handers.
The Rays now get to give more at-bats to outfielder Randy Arozarena, whom they acquired with Martinez in a trade this offseason.
Martinez, 32, is batting .239 with two home runs and 10 RBIs in 24 games this season with the Rays.
The Cubs may be in the market for some pitching after starter Tyler Chatwood left Sunday's game after 2 1/3 innings due to elbow discomfort. He will be evaluated on Monday's off day.
Chatwood already missed time this season with a back strain.