MILWAUKEE -- As if the Chicago Cubs didn't have enough to contend with -- including a scorching-hot Arizona Diamondbacks team nipping at their heels in the National League's wild-card race -- now they likely have to finish the regular season without last year's runner-up to the MVP, Javier Baez. A hairline fracture in Baez's thumb has thrust former All-Star Addison Russell into the spotlight.

Russell takes over for Baez in the Cubs' infield but is far from the player Baez is -- or even the player Russell once was. Russell undermined his once-promising career with his own problems away from the field, which led to an MLB suspension for domestic abuse. But now his team must count on Russell in a big way if it has any chance of making it to the postseason.

Despite hitting a home run, Russell failed in his first test as the regular shortstop. His throwing error in the ninth inning of a 2-2 game against the Milwaukee Brewers on Saturday led to the winning run for yet another crushing defeat for the Cubs on the road.

"Even though the ball was struck pretty well, I tried to take my time," Russell said after the game. "I just sailed it. In that situation, you have to be on point, especially where we're at during the season."

It was Russell's third throwing error from shortstop in three games, which suggests the Cubs might end up missing Baez in the field as much as they do at the plate. Russell and his manager say he just has to get used to the throwing angles from shortstop again.

Russell had better do it fast, as time is running out on the Cubs, who continue to plug leaky holes in their game. At some point, they might just drown -- likely leading to massive offseason changes that will turn over the 2016 World Series champions.

"It's a huge blow, what happened to Javy," Russell said. "I'm happy to step up and take on that role. I have a lot of confidence in myself and my ability."

Russell might have more confidence in himself than anyone watching in Chicago. Russell isn't exactly a fan favorite after his 40-game suspension for domestic abuse issues, which was completed at the beginning of the season. The Cubs stuck their necks out for him, hoping first and foremost he would rehabilitate himself -- and then he could help them on the field again. From a baseball perspective, they couldn't afford to get rid of Russell, as he was their only viable backup to Baez at shortstop in case the worst happened this season.

Well, the worst just did happen. And now Russell will have to step up his game, both at the plate and in the field. According to ESPN Stats & Information, when Baez is in the lineup this season, the Cubs' defense has a 73% out rate on ground balls to the left or up the middle. When Baez doesn't start, that rate drops to 65%. That percentage took yet another dip after Russell's latest miscue.

"Just working on arm angles," Russell said. "The feet are fine. The glove is fine."

And we haven't even discussed the mental mistakes Russell has made this season, including admitting to not being "familiar" with the signs. A lot is riding on Russell's shoulders, just as it was when the Cubs won the World Series. It seems like forever ago, but Russell was the starting shortstop in 2016 and made his only All-Star team that year.

"I believe if I just get to work and fully commit into that, I can go back to being the ballplayer I know how to be," Russell said.

Teammate Jon Lester offered his take.

"Addy is fine. He's a strong kid," Lester said. "We have the utmost confidence he can play shortstop for us. He did it for us before.

"It's not like we're calling up a kid that can't handle the situation."

Lester and the Cubs probably have more faith in Russell than most Cubs fans -- or perhaps they know they have to back him, by default. Manager Joe Maddon has no other options and doesn't want to put all the pressure on the 25-year-old infielder.

"We definitely have a lot of other good names," Maddon said. "It's not like we're just a one-man band. Other guys have to take care of their component of the game."

That's true. But none of them plays the most important position on the diamond and none of them is filling in for the energetic and spiritual leader of the team that Baez is. Baez has an energy that can't be replaced -- though the Cubs are just looking for few more solid throws to first. Three bad ones in three days is the stuff of Little League.

"Whatever reason, it's fading on him," Maddon explained. "We can fix that."

They had better. Time is running out, so it better be a quick fix. A division title seems further away than it has ever been, and now a playoff spot could be in jeopardy. The Cubs can't take on any more than they've brought on to themselves already. They showed faith in Russell, and now he needs to return the favor or the season won't end well.

"I believe it's pretty close," Russell said. "I just have to get in some work here and there and I'll feel good. My arm feels fine. I feel like I'm strong. Just have to get in a little extra work over there."