The Scotland full-back pulled out of Saturday's 2-1 defeat at Watford only hours before kick-off complaining of further pain from the injury which has seen him miss seven club games and three internationals this season.

The North End boss is hoping it is only a temporary setback and the player will be able to resume training this week.

But if the condition is worse than thought, and looks like keeping him out longer than the Championship's two-week break, then Irvine admits he may have to consider another loan just a week after borrowing Jay McEveley from Derby.

McEveley was one of only four defenders fit enough to play at Vicarage Road at the weekend.

Irvine had no back-up on the bench and admits that without Davidson he is unable to switch things round to halt a slump which has seen North End leak 10 goals in the last four matches – all defeats.

"Callum got a bang on his knee in training on Friday, but we thought he was fine," Irvine said as he looked back on a miserable trip to Hertfordshire.

>> Match report

"It was only on Saturday morning that he reported he was feeling something. So we had to go into the game with just four defenders.

"I can't change it if I want to. I don't have any others. This is the defence.

"We brought in Jay because we only had three. At the moment we have four. We have to find out how Callum is and we are hoping he will be fine.

"But at best we will have only five to choose from for the next game against Reading."

Full story in Monday's Evening Post