"Sean and Zak Whitbread are both making good progress," said Pearson.
"I wouldn't expect them to be out for too much longer now but they are not ready, they have not trained or played enough.
"There is absolutely no question of anyone being risked before they are ready to return.
"There was no chance of Sean being on the bench last week (against Middlesbrough).
"I would rather play with one sub than risk players who aren't ready. Sean is getting to a point now where he feels he is getting close."
St Ledger was not included in the 27-man squad for next week's friendly with Poland but Giovanni Trapattoni hopes to have the centre half back in time for the World Cup double header against Sweden and Austria in March.