CHICAGO | This is hardly the way the Royals wanted to head into their post-break schedule Friday night: having to scratch the biggest bat from their lineup.</p><p> Outfielder Jose Guillen was unavailable for the series opener against the Chicago White Sox after awakening early Friday with back spasms.</p><p> “He worked out three days in a row in a (batting) cage in Las Vegas,” manager Trey Hillman said. “It just started spasming up on him in the middle of the night and carried into this morning.”</p><p> Guillen contacted trainer Nick Swartz and reported early for treatment at U.S. Cellular Field. Hillman had Guillen in the original lineup before making the switch to insert Esteban German in left field.</p><p> Guillen is batting .270 and leads the Royals with 13 homers and 65 RBIs. “It’s not really the way we wanted to start out,” Hillman said, “having our No. 4 guy down. But it is what it is. Hopefully, we can get him ready for (Saturday).”</p><p>Six straight for Buck</p><p> It’s no longer a platoon situation at catcher. John Buck made his season-high sixth straight start Friday and appears in line to get the majority of playing time over Miguel Olivo for the foreseeable future.</p><p> “Game management,” Hillman explained. “I like what he does for us behind the plate as far as helping us read swings and helping the pitchers follow the game plan.</p><p> “Miggy will still mix in there, but I just feel that if we’re going to be successful, we need to be as consistent as possible with who is running our game. I believe Buck does a better job at that.”</p><p> Entering Friday, the Royals had a 4.21 ERA with Buck at catcher and a 5.17 ERA with Olivo. </p><p>Nuñez sharp in tune-up</p><p> Rehabbing reliever Leo Nuñez breezed through two innings Thursday night for Class AA Northwest Arkansas in what figures to be his final outing before rejoining the big-league club.</p><p> Nuñez started for the Naturals in their 9-4 victory over Arkansas and retired all six batters faced. He had two strikeouts and threw 16 strikes in 21 pitches.</p><p> “Very healthy,” Hillman said. “He was 91-96 mph and sitting at 93-94. He’ll continue to play catch, but he doesn’t have anything else definitive set with the Double-A club.”</p><p> Nuñez suffered a strained muscle in his upper back in a May 27 appearance against the Twins. He was 3-1 with a 1.71 ERA and seven holds in 21 appearances prior to his time on the disabled list.</p><p>Bale update</p><p> Lefty John Bale, the club’s other injured pitcher, is heading to Class AAA Omaha to continue his rehab assignment. He got roughed up a bit Thursday after following Nuñez in Northwest Arkansas’ victory.</p><p> Bale gave up one run and three hits while throwing 16 pitches in two-thirds of an inning. That followed an encouraging debut Tuesday when he worked one scoreless inning with two strikeouts against Arkansas.</p><p> “He was on a 20-pitch limit,” Hillman said. “They cut him off under instead of taking a chance by going another hitter and taking it 24-25. Everything worked just fine. I think he was at 88-89 mph.”</p><p> Plans call for Bale to boost his endurance to two innings by next weekend.</p><p> Bale was 0-3 with a 7.63 ERA in three starts before a fatigued shoulder forced him to the disabled list after an April 15 outing in Seattle. He delayed his return to active duty by suffering a broken hand when he punched a door May 2 in Cleveland. </p><p>Minor details</p><p> Third baseman Mike Moustakas served as the DH and went zero for four Thursday for Class A Burlington in his first game back after missing 10 days because of a slightly strained oblique muscle.</p><p> Moustakas, 19, was the second overall pick in the 2007 draft. He is batting .241 with 12 homers and 42 RBIs in 85 games.