Apparently Alfonso Soriano's cranky left knee was bothering him enough during his outfield play this past Friday that his plans to get an elective MRI (magnetic resonance image) in a few weeks got moved up to Saturday morning since he wasn't going to start today. In this video interview he says it's been sore for four months but with (approximately) 40 games left why can't he keep playing with the same pain? The pain seems to bother him more when he runs (rather than when he hits) so it's affecting his limited outfield abilities and I expect it's been a factor regarding his on and mostly off offense this season too.
Soriano was in no hurry to get the MRI as recently as this week. He originally expected to take the time to get it on their next day off, Sept 10th (after returning from the trip to NY and Pitt), but his limp became more noticeable after his game winning 3 run HR on Friday so they moved it up to Monday and when it was clear he couldn't start today they sent him for the test this morning.
Carrie Muskat from cubs.com reports that the MRI results just showed inflammation and the outfielder will likely get a cortisone shot (based on the manager's postgame comments) and be sidelined a few days. From the horses mouth, in the postgame interview, Lou Piniella said the team orthopedic specialist (probably Dr. Gryzlo) will look at Soriano on Sunday, and he most likely will get a cortisone shot to alleviate the pain.