The Chicago Cubs made three errors in last night's 4-3 loss to the San Diego Padres. Rookies Kris Bryant and Addison Russell committed two of them, but Starlin Castro's defensive mishap allowed the Pads to tie the game in the seventh inning.

Castro booted a ground ball hit by Matt Kemp and then Padres' outfielder Will Venable ripped an RBI single with two outs to tie the game 2-2. Addison Russell's error in the next inning eventually cost the Cubs the lead, but he's not a six-year veteran. In fact, he's playing in just 25 MLB games and is transitioning from shortstop to second base.

The error by Castro is much more concerning for a few reasons. With his seventh error of the season he's nearly halfway to his 2014 total (15) through just 38 games this season. He's now in his sixth MLB season with the Cubs and committing routine errors has been commonplace with him over the years. The 25-year-old started off the season seemingly more committed to his effort on defense, but it hasn't really worked out - his total defensive runs saved this season is -3, which ranks 22nd in the MLB.

Trade rumors have surrounded the Cubs because of their surplus of middle infielders. Will Castro emerge as the top candidate to be traded if his defensive woes continue, especially since Javier Baez is making strides at Triple-A Iowa?

"What's the stepping stone for Castro? There's no doubting he cares, but for every few spectacular plays he makes on defense there's always the routine error," writes Jesse Rogers of ESPNChicago.com. "No one is saying the Cubs should make a move now, but Russell's worth diminishes at second while Castro simply isn't in Russell's league at shortstop ...

"This isn't about disliking Castro, it's simply about what is best for the Cubs moving forward. If there was no Russell you would have no choice but to live with Castro there. But the Cubs will have a choice."

It's previously been noted the Cubs view shortstop as the best position for Russell, which further creates speculation of Castro being dealt before the deadline. The shortstop is under a team-friendly contract and would likely provide the best return in a trade because he's proven what he's capable of at the MLB level despite also displaying his shortcomings.

Additionally, after a poor audition last season and an awful offseason, Baez has rebounded in the minors and is now batting .296/.375/.423 with six runs scored, two home runs and 10 RBIs in 19 games. It was originally believed the Cubs may have to hold onto their current cast of middle infielders because of Baez's fall from grace, but that has now changed.

"Of course, he's on the radar. He's always on the radar," manager Joe Maddon told Patrick Mooney of CSN Chicago. "When is he going to get here? I'm not 100 percent sure. But everything's going well right now."

Again, it's all speculation at this point, but one can't help but think what the Cubs will do if Castro continues on this path.