St. Ledger has been sidelined since suffering the injury in the 2-0 npower Championship victory at home to Bristol City at the start of October.
The problem forced him to pull out of the Republic of Ireland squad for their World Cup qualifying matches against Germany and Faroe Islands that month, and he has missed the Foxes' last three league fixtures.
St. Ledger reckons he will be back around mid-November but Pearson is refusing to put a timescale on the 27-year-old's return, insisting the player will not be rushed back into action.
"He has responded very well to treatment, but the bottom line with any injury is that it will take as long as it takes," said Pearson in his pre-match press conference ahead of Saturday's trip to Watford.
"We are not in a position where we are going to rush him. It is the same criteria applied to everyone - when players are back, I want them to stay back. I am not prepared to rush players back one game early if it is going to put in jeopardy their availability during a sustained period."