Finn had been tipped to step up his recuperation from a thigh strain by practising in the nets yesterday but did not bowl, leaving Prior resigned to his likely unavailability in Ahmedabad.
Fellow paceman Stuart Broad did manage six overs off his full run, however, and Prior believes England have enough talent in reserve for Alastair Cook's challenging baptism as permanent Test captain.
"The one thing you would say is, if there was a realistic chance of Finny playing, then he probably would have had a long bowl today," said Prior. "It's a setback. I'm sure coach and captain would want to be able to choose from every player that's out here. But we have a lot of strength and depth. It's one thing that's made our squad so strong over the last couple of years. If Finny's not available, there's another guy that can step in and do as good a job - that's the way we look at it."
Yorkshire's Tim Bresnan is favourite to join James Anderson and Broad in England's pace attack if Finn fails to make a dramatic recovery, while Durham's Graham Onions is the other candidate.
All-rounder Samit Patel is thought likely to help Graeme Swann with spin bowling duties, although former India captain Rahul Dravid believes England selectors should pick Monty Panesar instead.
"Bits and pieces cricketers haven't had much of an impact in India," Dravid said, referring to Patel. "Monty has bowled well in India in the past and can keep one end tight so I would like him to play. Personally I would definitely play the two frontline spinners. Indians are extremely good players of spin and they are not going to get out to part-time bowlers."
Patel has impressed with bat and ball during England's three warm-up fixtures, pushing him ahead of leftarmer Panesar in the pecking order for the four-match series.