The results of the MRI were not immediately available, but when asked whether he interpreted it as bad news, manager Charlie Manuel said, "Yeah. Evidently the doctors definitely thought he should go get an MRI."
Polanco was unavailable Monday, which forced backup catcher Erik Kratz to pinch-run for Ryan Howard to score the winning run in the ninth inning. He sat Tuesday for the third time in four games.
It's problematic timing for the Phillies, who could look to move Polanco to a contending team before the July 31 deadline. Polanco has a $5.5 million mutual option for 2013 that will not be exercised. He has about $2 million remaining on his contract for 2012, plus a $1 million buyout for the option.
There were recent reports of the Baltimore Orioles' showing interest in Polanco. If the back pain is even remotely an issue, it will kill whatever (limited) trade value he would have.
Entering Tuesday, the Phillies had received the least production in the National League from their third basemen. Their .599 OPS at third was better than only the Oakland Athletics' and Chicago White Sox'. Major-league third basemen have averaged a .742 OPS in 2012.
If Polanco misses extended time, the Phillies will be giving up defense but adding offense with a Ty Wigginton-Mike Fontenot combination.
It remains a position without an answer for 2013. The free-agent market lacks legitimate options. Internally, there are no options close to being major-league ready.
"If you go look, around baseball third base is a position that has changed," Manuel said. "It used to be a prototypical third baseman was a big RBI guy who had a pretty good glove, arm, and some power. . . . A big prototypical third baseman is hard to find. There are still some."
After a pitch off his right elbow limited Shane Victorino to one inning Monday night, the centerfielder was back in the Phillies lineup Tuesday.
Victorino said he briefly lost feeling in his right arm, and Manuel indicated the ball had hit near "his crazy bone." Victorino wore a large wrap around the elbow and participated fully in pregame practice.
"It feels fine," Victorino said. "I'm ready to go."
Victorino remains a trade target, and three interested teams - San Francisco, Pittsburgh, and Los Angeles - had scouts watching Tuesday.
Monday was the first time Chase Utley and Ryan Howard hit back-to-back home runs against a lefthanded pitcher. The two have batted next to each other for much of the last five years and have connected on back-to-back homers three other times. . . . Outfield prospect Domonic Brown missed his second consecutive game for triple-A Lehigh Valley with an aggravated knee injury. He is expected to return this week. . . . Catcher Brian Schneider (ankle) began an official rehabilitation assignment Tuesday with single-A Clearwater and served as designated hitter. . . . Lefthander Raul Valdes (hip) will begin a rehab assignment with double-A Reading on Wednesday. . . . Outfielder Jason Pridie, designated for assignment Sunday, was outrighted to triple-A Lehigh Valley.
Contact Matt Gelb at firstname.lastname@example.org. Follow @magelb on Twitter.