The Rangers have told reporters that the slugger has some soreness in his chest area and the tests are precautionary.
"Nelson Cruz has what we believe to be a muscle strain in the chest," assistant GM Thad Levine said (MLB.com). "We've just sent him to the hospital to do a battery of tests just to make sure it's not more serious than something muscular."
Cruz, 32, hit .260/.319/.460 with 24 homers, 90 RBI and 86 runs last season. He's on the roster for the Dominican Republic in the upcoming World Baseball Classic.
UPDATE: The Rangers have issued the following statement:
Rangers outfielder Nelson Cruz underwent a full battery of tests this morning at Del Webb Medical Center in Surprise after experiencing pain in his chest early this morning. The results of all tests have been negative. Cruz is expected to be released after completing a stress test and is expected to resume baseball activities as early as Saturday.
UPDATE: The AP reports Cruz has been cleared of more serious issues and can indeed resume baseball activities on Saturday.
For more baseball news, rumors and analysis, follow @EyeOnBaseball on Twitter, subscribe to the RSS feed and "like" us on Facebook. Also, individually interact with us on Twitter: @MattSnyder27, @daynperry and @mikeaxisa.