CHICAGO -- It took Ken Williams one word, with a little extra energy for emphasis, to answer the following question when asked of him on Friday: Will manager Rick Renteria and his staff be able to run a good team pushing for the playoffs, such as the White Sox in 2020 or '21?
"Absolutely," Williams told MLB.com.
That strong show of support from the White Sox executive vice president doesn't exactly lock down long-term contracts for Renteria and each of his coaches. But there's little doubt Williams and the front office appreciate the job done by these gentlemen during a long, tough 2018 season as part of the rebuild.
Williams made a point of praising the entire group.
"It's the entire coaching staff who is here on most night games in the morning or closely before noon," Williams said. "They are working tirelessly to try to win that night's game."
The White Sox 44-76 record entering Friday night's series opener against the Royals doesn't matter nearly as much to Williams as the approach taken by Renteria and his staff. Their day not only is filled with hard work, per Williams, but good work as well.
"Here's what I will say: I know it doesn't always show in the results, but I think they are great teachers, they are great communicators and they are great leaders all in their own right," Williams said. "They sincerely care, from the first guy on the roster to the 25th guy to the guys we bring up from the Minor Leagues and on down.
"They commit their time, their energy, their patience. I cannot say enough about the effort of these guys."
Castillo begins rehab assignment
Welington Castillo started his injury rehab assignment for Triple-A Charlotte on Friday by going 1-for-4 with a strikeout and a walk as the designated hitter in a 4-3 loss to Louisville in 10 innings.
The White Sox catcher, who agreed to a two-year, $15 million deal with an option for 2020 prior to this season, is working his way back from an 80-game suspension received without pay after testing positive for Erythropoietin (EPO), a performance-enhancing substance, in violation of Major League Baseball's Joint Drug Prevention and Treatment Program. The 31-year-old Castillo is eligible to return on Thursday.
"Hopefully he's healthy and continues to be the same as it's been," Renteria said. "He was managing all of our starters. We'll see how he's doing when he gets here and then we'll move forward."
Renteria has exchanged a few notes with Castillo in his absence to see how he's doing.
"He went through a lot of his routine the last couple of days," Renteria said. "He'll be in the lineup DHing to start. Probably get a game of four or five innings behind the plate and then stretch it out like we would do it in Spring Training."
Leury Garcia returns
Prior to Friday's series opener against the Royals, outfielder Leury Garcia was reinstated form the 10-day disabled list. He takes the roster spot of outfielder Ryan LaMarre, who was optioned to Charlotte following Wednesday's 6-5 victory over the Tigers.
Garcia was not in Friday's starting lineup after working his way back from a left hamstring strain. His versatility becomes valuable with the White Sox playing 20 games in 20 days before their next off-day on Sept. 6.
"You'll see him playing center, left, right, the infield," Renteria said. "We're going to have a 20-day stretch now where I'm going to have to give some of these guys a blow.
"We tried to start it in Detroit, giving some of these guys some rest. We were able to give [Tim Anderson] back-to-back days. Leroy has been a big part of how we were moving forward and I'm sure he'll have plenty of opportunities."
Kopech flourishing at Charlotte
• Michael Kopech, ranked as the White Sox No. 2 prospect by MLB Pipeline, is 4-0 with a 1.84 ERA over his past seven starts for Charlotte. He also struck out 59 and walked only four during that stretch, including nine strikeouts without a walk on Thursday against Louisville.
Kopech sits at 170 strikeouts over 126 1/3 innings and 24 starts this season. His career highs were set last year with 25 starts, 134 1/3 innings and 172 strikeouts.
• Pitching coach Don Cooper held a clinic on Friday morning at Guaranteed Rate Field for approximately 15 pitchers from the White Sox Amateur City Elite (ACE) youth baseball program.