The Cubs acquired another arm for the bullpen Tuesday, trading for Nationals right-hander Henry Rodriguez for a Class-A pitcher. Rodriguez was designated for assignment by the Nationals last week after going 0-1 with a 4.00 ERA in 17 relief appearances. The Cubs sent Kane County right-hander Ian Dickson to the Nationals and designated Triple-A Iowa pitcher Eduardo Sanchez for assignment to make room for Rodriguez on the 40-man roster. Sanchez was 0-1 with a 9.82 ERA after being claimed off waivers from the Cardinals on May 21. Cubs manager Dale Sveum said reliever Zach Putnam would get an MRI on his right elbow Wednesday after leaving the game Tuesday with soreness. Putnam likely is headed for the disabled list, with Rodriguez taking his spot.