Marsh was diagnosed with a right middle finger sprain following his removal from Tuesday's game against San Diego, Paul Casella of MLB.com reports.
Marsh suffered the injury sliding back into first base while getting picked off in the first inning. He's slated to undergo further evaluation, and a timeline for his return will likely take shape once the Phillies get his results back. He can be considered day-to-day in the meantime, though Edmundo Sosa could be in line for extra starts in the outfield if Marsh has to sit.