Wellens has not trained since limping off in the second half of last week's 3-3 draw at Watford with a hamstring injury.
He underwent a scan on Monday to determine the severity of the injury but could yet be passed fit to face the Lilywhites.
Andy King is on standby to replace Wellens alongside Matt Oakley in the middle of the park but the Foxes have no other major concerns.
Pearson said: "If Richie is missing he is missing but again he is one player in the squad and we have a decent squad here. If he misses out it is another player's opportunity."