Per Anthony Andro of the Fort Worth Star-Telegram, the Rangers have purchased the contract of right-hander Mark Hamburger from Triple-A Round Rock, have recalled Leonys Martin from Round Rock, and have placed Nelson Cruz (left hamstring) and Darren O'Day (right shoulder inflammation) on the 15-day disabled list.
A 40-man roster move to accommodate Hamburger's addition to the roster is still forthcoming, and, if I were to offer an educated guess as to what that move will be, I would suggest that Wilmer Font -- who is out for the season after undergoing Tommy John elbow ligament replacement surgery last October -- will be transferred to the 60-day disabled list. Failing that, one of Ryan Tucker or Tim Wood could end up being placed on outright waivers for the purpose of moving them off the 40-man roster.
Update: Per ESPNDallas.com's Richard Durrett, the Rangers have released Ryan Tucker outright to clear room for Hamburger. Tucker struck out the side on 14 pitches in an inning of work at Oakland back on April 29th, but then allowed at least one run in each of his next four appearances, and was optioned back down to Round Rock back on May 18th. In 68.1 innings pitched at Round Rock, Tucker posted up a 5.40 ERA in spite of otherwise decent peripherals (8.4 K/9, 4.1 BB/9, 0.7 HR/9); however, the end of his Pacific Coast League run was marred by his allowance of at least five earned runs in three of his last four starts with the Express, and so away he goes.