This season, Kubel posted a slash line of .220/.288/.324 as he battled a variety of leg ailments.
"It's still baffling what happened to him," Towers said. "He had such an incredible three-quarters of a season last year and then really wasn't the same player."
Kubel was dealt Friday to the Indians along with cash considerations in exchange for a player to be named later or cash. The player the D-backs will likely receive in the deal is "a guy that more than likely will come up here in September," Towers said.
The D-backs saved about $200,000 in the deal.
Steve Gilbert is a reporter for MLB.com. Read his blog, Inside the D-backs, and follow him on Twitter @SteveGilbertMLB. This story was not subject to the approval of Major League Baseball or its clubs.