Nate McLouth was still out with an undetermined illness, forcing the Pirates to send Steve Pearce down to Triple-A Indianapolis and keep Nyjer Morgan, the club's only other primary center fielder.
"With Nate gone, we really didn't have an everyday center fielder," Russell said. "Nyjer has been playing well. Unfortunate circumstances -- it wasn't that Steve failed or Steve did a bad job. It's just a situation, with a 25-man roster, we need a center fielder. [Jason] Michaels can play there, but Nyjer's a center fielder."
McLouth, who hasn't played since Monday, may have to wait five more days for results on blood tests taken on Thursday, though he could come back before then. An earlier test for mononucleosis came back negative. McLouth was expected to meet with doctors again on Friday, but there's no timetable for his return.
"His throat's still really sore, but the achiness is starting to feel better," Russell said. "So we're hoping it's not a long-term thing. He didn't look very good the last couple days."
Morgan, who went 1-for-7 in two starts in St. Louis, made his third straight start in center on Friday. Morgan was recalled from Triple-A when Mientkiewicz was placed on bereavement on Monday.
Pearce, the organization's 2007 Minor League Player of the Year, batted .218 (12-for-55) with seven RBIs in 16 games after being recalled from Indianapolis on July 26.
Nick Zaccardi is an associate reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.