The Diamondbacks are the only NL West team that has not shown interest in Marlins right-hander Ricky Nolasco.

Why?

The D-backs are not interested in “renting” a potential free agent — and if they acquire a starting pitcher, they will want him to be a significant upgrade over their major league-ready prospects, sources say.

Two starters, in particular, interest the D-Backs, according to sources. One, Brewers right-hander Yovani Gallardo, is available. The other, Cubs right-hander Jeff Samardzija, only could be had for an “overwhelming” package — and the two clubs have not engaged in discussions, sources say.

The Diamondbacks entered Thursday ranked 11th in the NL with a 4.17 rotation ERA. Their best pitcher, left-hander Patrick Corbin, is in his first full season. The addition of a top-of-the-rotation starter would significantly enhance the team’s chances in the hotly contested NL West.

The D-backs, though, aren’t prepared to move on any pitcher just yet.

They are waiting to see if right-hander Brandon McCarthy returns from shoulder inflammation before the July 31 non-waiver deadline, while monitoring several active members of their rotation as well.

Righty Trevor Cahill has a 9.30 ERA in five starts in June. Lefty Wade Miley has recovered in June after a rocky May. Righty Randall Delgado has averaged six innings and produced a 3.75 ERA in his first two starts.

Lefty Tyler Skaggs, who returned to Triple A after struggling in two of his three starts, represents another internal option. But the struggles of righty Ian Kennedy, who has a 5.21 ERA, and re-injury to righty Daniel Hudson, who recently underwent a second Tommy John surgery, could persuade the D-Backs to seek external solutions.

Gallardo, 27, is under contract for $7.75 million this season and $11.25 million next season, with a $13 million club option for 2015. He currently is sporting a 4.20 ERA, but has pitched better in June.

The Brewers, while willing to move Gallardo, likely will ask a high price for giving up two-plus years of club control. The Dodgers and Rangers are among the other clubs that could pursue Gallardo, who — as a native of Mexico — would offer added marketing appeal to those teams as well as the Diamondbacks.