MILWAUKEE -- Javier Báez had every intention of playing against the Brewers on Thursday. That was before the Cubs' shortstop continued to feel pain in his left thumb during a pregame round of batting practice at Miller Park.

Baez arrived to the Brewers' ballpark on Friday and tried swinging a bat again, and again the discomfort persisted. Now, the Cubs are sending Baez back to Chicago, where he will undergo an MRI exam on his left hand on Saturday morning to examine whether there is more to the ailment than just a jammed thumb.

"Just to make sure we know what we're dealing with. That's it," Cubs manager Joe Maddon said prior to Friday's game in Milwaukee. "When he came in, he tried to swing it a little bit, but it still didn't feel right. So, as opposed to just continually waiting, we just need to find out for sure what we're dealing with."

The injury occurred on Sunday, when Baez stole second base in the third inning of a 4-0 loss to the Brewers at Wrigley Field. On the play, Milwaukee shortstop Orlando Arcia made a hard tag on Baez, whose thumb was stretched as he contorted his body. Baez initially remained in the game, but he exited by the sixth inning.

Baez sat out the next two games against the Mariners at home and missed the first two of the Cubs' current four-game series in Milwaukee. Given the shortstop has tests slated for Saturday, Maddon said it is unlikely that Baez would return to the lineup until Sunday at the earliest, if he is cleared to resume playing this weekend at all.

Following the series against the Brewers, the Cubs head west for a four-game road set against the Padres in San Diego.

Maddon reiterated that he has no issues with players sliding head-first on similar types of plays.

"I'm fine with it," Maddon said. "It happened. He got hurt. He could get hurt sliding feet-first, too. He could've gotten hurt getting out of his car. There's so many different ways to get hurt. I don't really worry about that. I don't like when people slide head-first at home when the catcher's got the ball. That's when you're going to get hurt. But this other stuff ... it happens. It's part of the game."

While Baez is out, Addison Russell is Chicago's primary shortstop with utility man David Bote serving as the backup.

"Addison's a wonderful shortstop in his own right," Maddon said. "He probably doesn't have the same offensive pedigree that Javy does, but he can play shortstop with anybody, Addison can. I'm just going to wait until [Saturday] and see what they say and then we'll figure out what the game plan actually is."

Losing Baez -- the runner-up for the National League Most Valuable Player Award a year ago -- for any length of time is a big blow for the Cubs, especially down the stretch in a postseason chase.

Through 133 games played this season, Baez has hit .281/.316/.532 with 29 home runs, 38 doubles, 85 RBIs and 88 runs scored for Chicago. At shortstop, he has compiled 15 Defensive Runs Saved (third in the Majors among qualified shortstops) and 15.3 Defensive Runs (first among MLB shortstops, per Fangraphs), with an 8.8 UZR/150 (fourth).

"He's very important. My goodness," Maddon said. "The thing you're looking at there is he's been a little bit off of his game offensively, knowing that he's going to get back on it at the right time. That's been in the back of my mind throughout this whole moment for him. But, it is what it is."

To Maddon's point, Baez has hit .200 with a .603 OPS over his past 20 games, during which his season OPS has dropped from .886 to .848.

"Personally," Cubs president of baseball operations Theo Epstein said on Thursday, "I always feel like he's one swing away from catching fire and can change the face of our lineup when he gets hot. He contributes in so many different ways."