OAKLAND, Calif. -- Rougned Odor began a rehab assignment Wednesday. Ronald Guzman isn't far behind. The infield could be back at full strength within a week.And when that happens, the Rangers will have a tough decision looming.They will either have to part ways with one of two backup infielders who have proven valuable in their surprisingly strong start or they will have to trim the bullpen to seven relievers, which seems almost unthinkable since the starting rotation is struggling to get into the middle innings of games.At the center of this is spunky 28-year-old infielder Danny Santana, whose contract was purchased when Odor was hurt.