Mckenna has been suffering through injury since early January when he was playing through the pain barrier with a hernia. The midfield man had an operation in Germany which was set to see him return in March but unfortunately persistent problems to his groin have prevented Mckenna from stepping up his training.
The blow is a big one for Preston who have relied on a makeshift midfield for the majority of the second half of the season. Simpson will be hoping that Davidson remains fit for the remainder of the season so he can continue his good form which has seen Preston pick up some positive results.