"The Giants began Sunday by celebrating their pitching. They ended the afternoon worrying about it.Randy Johnson departed after 3 2/3 innings with a strained left (throwing) shoulder, establishing the subdued tone of the Giants' 7-1 loss to the Houston Astros.Johnson's immediate pitching status is uncertain. He's expected to undergo an MRI on Monday, which could reveal the extent of his injury.If Johnson has to miss a start, it would mark a rare encounter with adversity for the Giants pitching staff, who placed Matt Cain and Tim Lincecum on the National League All-Star squad before the game. No member of the starting rotation has missed a turn this year due to injury.Manager Bruce Bochy assured that the Giants wouldn't be hasty with Johnson, 45."If there's anything going on, we'll give him some extra [rest]," Bochy said.Johnson provided no additional insight into his condition."It's a strain," he said. "I'm getting an MRI. That's all I have to say."Fortunately for the Giants, they could use next week's All-Star break to their advantage. Johnson could rest and recover for as many as 15 days -- the length of a disabled-list stint -- and miss just one start.If the Giants place Johnson on the disabled list, a possible spot starter would be right-hander Joe Martinez, who was scheduled to pitch Sunday for Triple-A Fresno. Martinez made the Opening Day roster as a long reliever but was sidelined with a concussion and three fractures after being struck in his forehead by a line drive off the bat of Mike Cameron in the season's third game."