BALTIMORE, AUG. 3 -- Right-hander Dave Johnson, the Baltimore Orioles' winningest pitcher, will have a series of tests Saturday to determine the source of the spasms he suffered in his back and legs during Thursday night's 5-1 victory over the Kansas City Royals.

Johnson (11-6), who was removed by Manager Frank Robinson with two outs in the sixth inning after limiting the Royals to three hits and a run, was examined today by back specialist Hank Dudley and trainers Richie Bancells and Jamie Reed. He is scheduled to get X-rays and an MRI (magnetic resonance imaging) test Saturday.

"Things are going real well for me," Johnson said. "I feel like the club is counting on me to be in there.

"This way {with tests}, we'll know for sure right away. Hopefully this thing will be something real minor."

The Orioles hope so too. With last year's top two starters, Jeff Ballard (bullpen) and Bob Milacki (disabled list), no longer in the rotation, Johnson, a career minor-leaguer until his Aug. 1 call-up in 1989, has emerged as the ace of the staff.

Johnson, tied for seventh in the American League in victories, has allowed just four earned runs in his past three starts, posting a 1.86 ERA and a 3-0 record.

"He still is a real battler," Robinson said. "He does it in the course of a ballgame. He went back out {Thursday} for the fifth and sixth. After he had the win, it would have been very easy for him to say 'My back's cramped up, take the ball.' "

Staff Minus One

Because right-handed reliever Brian Holton was put on waivers today to make room for newly acquired outfielder Dave Gallagher, Robinson's pitching staff is down to 10. But Robinson said an 11-man staff is more luxury than necessity.

"It changes the role of one or two pitchers," Robinson said. "Now {Curt} Schilling will have a few more innings and have to warm up a little earlier, and so will {Mark} Williamson. But it won't affect the way I manage the game." . . .

Third baseman Craig Worthington, whose single scored Cal Ripken with the Orioles' fourth run Thursday night, did not start today after straining his right hamstring running out the hit. Worthington, replaced in the lineup by Tim Hulett, is listed as day to day. . . . For Monday's Hall of Fame game against the Montreal Expos, Baltimore will add five players from its minor league system: pitcher Dan Boone, infielder Jeff McKnight, catcher Mike Eberle from Class AAA Rochester; pitcher Mike Cavers from Hagerstown (AA); and pitcher Todd Stephan from Frederick (A). . . . George Brett's next double will be No. 543 in the Kansas City first baseman's career, moving him into 11th place all-time. Of the 10 players who rank higher, only Pete Rose, second with 746, is not in the Hall of Fame.