Preston's promotion bid has been hit by a double injury blow with Simon Whaley set to miss the rest of the season and Paul McKenna possibly facing surgery.
Preston boss Simpson's squad has been training in Spain
Midfielder Whaley broke his big toe on the club's Spanish training camp after a coffee table marble top fell on it.
"It could mean him being out for the rest of the season," Preston boss Paul Simpson told the club's website.
McKenna is due to see a specialist on Thursday to decide whether the midfielder requires groin surgery.