SAN FRANCISCO — As the Giants attempt to turn their season around, they’ll have to do so without their ace, at least for a couple of weeks. Logan Webb went on the injured list with right knee bursitis on Saturday, a few days after he was removed after just four innings because of the discomfort. Webb was replaced on the active roster by Trevor McDonald, who is expected to start against the Los Angeles Dodgers on the next road trip.Webb was supposed to face Yoshinobu Yamamoto on Monday at Dodger Stadium, but the Giants are hopeful the break will allow the discomfort to clear up and prepare him for the final four-plus months of the season. The knee issue is something Webb has been able to pitch through in recent years, but he has had trouble fully utilizing his delivery and getting the ball to certain parts of the strike zone this season. Webb will be eligible to return to the rotation on May 21 and the expectation is that he’ll need the minimum amount of time on the IL. Giants manager Tony Vitello said Friday that he expected Webb to make his next start, but part of that was just the fact that Webb generally pitches through some sort...