How many teams are in the running is uncertain, as Tanaka and his agent, Casey Close, have kept the process confidential, but the D-backs are reportedly one of his finalists.
"Out of respect for the process, I'm not going to get into any specifics," Towers said. "Casey has been very forthright and open, and it's been a really good process. I think everyone has been treated equally and fairly."
Varying reports have the D-backs offering Tanaka a six-year deal worth more than $115 million. In addition, the team he chooses to sign with would owe his Nippon Professional Baseball team, the Rakuten Golden Eagles, a $20 million posting fee.
The D-backs have sought a front-line starting pitcher throughout the offseason, and after kicking the tires on the Rays' David Price and the Cubs' Jeff Samardzija, decided to make a hard push for Tanaka.
If they don't land Tanaka, the D-backs will likely stick with their current cast of pitchers. Towers has said that he does not anticipate offering more than a three-year deal to any of the top free-agent pitchers out there, and given the way the market is shaping up, it will take more than that to sign one.
Without Tanaka, the D-backs would enter Spring Training with a rotation of Patrick Corbin, Wade Miley, Trevor Cahill and Brandon McCarthy, with Randall Delgado and prospect Archie Bradley among those competing for the No. 5 spot.
For now, though, the D-backs wait like everyone else.
"I do think, because of the timing standpoint, that we're probably late in the fourth quarter," Towers said.
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.