D-backs team president/CEO Derrick Hall said that nothing has changed over the last two years.
"We've always said that if a team wants to talk about any of our players, including Justin Upton, that we would listen," Hall said. "We owe it to our fans to look at all ways to improve our team."
Towers acknowledged he has had talks regarding Upton.
"He will not be an easy guy for us to move," Towers said. "I think we've said it's probably unlikely we end up doing something with him, but if somebody is willing to step up and we think it's a deal that's going to make the Diamondbacks better next year and going forward, we'll talk about trading him."
Rosenthal's report cited a source as saying the chances were "80-20" Upton would be playing somewhere else next year.
"I'd like to point out that this has been going on for a couple of years now and we haven't traded him," Hall said.
Towers declined to put odds on whether Upton would be moved. There is hesitation in trading a player who just turned 25 in August and has to potential to be an elite player.
"I've certainly got pause," Towers said. "I'm not looking just to move him. We've got some areas of need that if we can address multiple areas with our outfield depth, then we'd consider it. I thought there were parts of his game that really got better last year: pitch recognition, walks, still scored over 100 runs, better contact. At his age, his power is going to come back. I think that's why people have interest in him. They're saying, 'Hey this is a time to strike, buy low, his power numbers are down.' There's no doubt that the power will come back."
If the D-backs do deal him, they are looking for proven Major Leaguers in return, not prospects.
"We would have to have a legitimate everyday player or a legitimate, top-end-of-the-rotation type starter," Towers said. "If not, we're better off, I think, keeping him."
Upton is due to make $9.75 million next year, $14.25 million in 2014 and $14.5 million in '15.
Another report, this one by ESPN's Jerry Crasnick, said the D-backs were open to listening to offers for right-hander Trevor Bauer.
"I'm sure there are teams that are interested in [Bauer]," Hall said. "And, again, we're willing to listen, but it's not like we're out there shopping him."
Bauer was the team's first-round pick (No. 3 overall) in the 2011 First-Year Player Draft and made a rapid rise through the farm system.
"I don't know where that came up," Towers said. "We're not shopping Bauer. After moving [Jarrod] Parker last year, it'd be nice to keep all of our pitching depth if we can. People hit us on outfielders and pitching. That's where we have depth. Those are areas where we have depth. But we're not trying to move Trevor Bauer or shopping him at all."
Bauer struggled in four starts in the big leagues last season, and there was friction between him and catcher Miguel Montero. The organization also appeared to want him to change his intense pregame throwing routine, as well as his style of pitching.