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8/22/2013 10:47 P.M. ET

Cubs hoping Lake's glove work follows his bat

CHICAGO -- There's never been much of a question about Junior Lake's offensive gifts, which have been on display since he was called up to the Majors on July 19. Now, as he grows more accustomed to playing the outfield, the Cubs hope the defense will follow.

Lake, the Cubs' ninth-ranked prospect according to MLB.com, rose through the Minors as an infielder but has played only outfield (19 games in left and 16 in center, including Thursday's start against the Nationals) with the Cubs, particularly with injuries to Brian Bogusevic and Ryan Sweeney, and the departure of David DeJesus. He has made three errors (all in center) and has one outfield assist in 66 chances.

"He brings a lot to the table," manager Dale Sveum said. "He brings a lot of energy to make guys do things. But he can hit the ball out of the ballpark, he can get doubles like he did [on Monday], a ball off [Ryan Zimmerman] and stretch it to a double. That kind of speed, athleticism, power is what you want to fill your team with."

Lake, who has doubled in four straight games entering Thursday, is the first Cubs rookie to achieve that feat since Starlin Castro on Aug. 22-25, 2010. He has multi-hit games in three of his last four, and entered Thursday leading all Major League rookies with 42 hits since his debut on July 19.

Overall, he's hit safely in 23 games, and has 12 multi-hit games in his first 32 big league contests. Lake, who was signed as a non-drafted free agent in February 2007, hit .295 with 10 doubles, two triples, four home runs, 18 RBIs and 14 stolen bases in 40 games with Triple-A Iowa this year.

Lake, who went 1-for-4 with a walk and a run, fielded nine putouts cleanly in Thursday's 5-4 loss to the Nationals in 13 innings.

With Castro manning shortstop on an everyday basis, Lake is likely to get the most looks in center or left. And Wrigley Field, with the wind and strange caroms that balls can take off the ivy-covered walls, is no easy place to learn the outfield.

"More than anything, it's the defensive part of it right now," Sveum said. "Just getting comfortable and getting as many reps as possible in center field and in the outfield, as much as anything. Obviously, the hitting stuff -- right now, he's a cut-and-slasher, but you see him even laying off and taking pitches and getting better at that. That kind of gradually comes with the better starting pitching he's going to face. He's already been here about a month now to see what big league pitching is, and you can see he's handling it pretty well."

Injured Cubs to begin work in Arizona

CHICAGO -- Outfielder Ryan Sweeney and third baseman Luis Valbuena will head to Arizona this weekend to begin rehab work, and starting pitcher Scott Baker will continue his on Friday with Class A Kane County.

Sweeney and Valbuena will both travel to Mesa on Friday, where Valbuena (right oblique strain) will begin taking batting practice from coaches and Sweeney (fractured left rib) will begin playing in Arizona League games on Saturday.

Valbuena has been on the disabled list retroactive to Aug. 3, while Sweeney has been out since the end of June. Baker, recovering from Tommy John surgery, has not appeared in a game this season.

The right-hander made two starts for Class A Advanced Daytona (six hits, two earned runs, two strikeouts, two walks in 6 1/3 innings) and three for Kane County, where he's struggled, allowing 13 runs on 17 hits and six walks in 8 2/3 innings, with five strikeouts.

Cubs mulling prospects as September callups

CHICAGO -- The Cubs have acknowledged that the next five weeks will be about getting their 40-man roster healthy and in a good position to build on into next season. More of that will come into focus as the team thinks about September callups and which of its top prospects -- if any -- could join the club.

Manager Dale Sveum said on Thursday that he has had some discussions with president of baseball operations Theo Epstein and general manager Jed Hoyer about which players may join the expanded roster, but it's "nothing concrete."

Ryan Sweeney and Luis Valbuena are expected back from injury around that same time, and Sveum said he doesn't see anybody coming up who isn't on the 40-man roster, except maybe an extra catcher.

"The [Brian] Bogusevics and Sweeneys, and obviously [Donnie Murphy's] doing a heck of a job," Sveum said of the outlook for current roster players. "And yesterday's topic was getting [Anthony] Rizzo and [Starlin] Castro to where they go into the winter feeling a heck of a lot better than they did two days ago."

That likely means top prospects Javier Baez (with Double-A Tennessee) and Albert Almora (Class A Kane County) are likely out of the picture. In 119 games between Daytona and Tennesee this season, Baez has hit .286 with 33 home runs and 100 RBIs.

"It's hard to do in [that many] games," Sveum said. "Remember, we get 20 more games than they do … to have a chance at 40 [home runs] in those leagues, in the Southern League and Daytona, it's not the easiest parks and leagues to hit home runs in. It's impressive, and the 100 RBIs is another impressive stat."

Does that mean he could come up in a few weeks?

"The numbers, sometimes guys do put you in situations where you do start thinking about it, but those are obviously questions and stuff that have to be dealt with with Jed and Theo," Sveum said. "But I don't see that happening."

No. 3 prospect Jorge Soler and No. 5 prospect Mike Olt are both on the 40-man roster.

Joey Nowak is a reporter for MLB.com. Follow him on Twitter at @joeynowak. This story was not subject to the approval of Major League Baseball or its clubs.