The Republic of Ireland international was a notable absentee – along with midfielder Kevin Nicholls – when the squad returned to work this week, sparking fears his long-standing back problem had flared up again.

But Irvine has assured fans Henderson is only 'a little' behind schedule and should be joining in soon.

And he has also revealed that Nicholls, who had knee trouble towards the end of last season, is not a major worry either.

Henderson has been out of action for more than 10 months after damaging a disc in his spine.

"Wayne's not been able to start with the rest of the lads, which is a shame," he said.

"But he's getting close. We are hopeful the treatment he has had during the close season means his problems are now behind him.

>> PNE return to training: Video report and photo gallery

"The initial target was for him to be fit for the first day of pre-season on Tuesday, but he is a little behind that at this moment in time. Hopefully he will be able to join in full-time training with the squad soon and then, from there, he will play his first game for us."

Henderson was crocked after playing the first four games of last season.

Initially it was thought he had a simple slipped disc, but the problem continued for weeks and, despite injections to try and speed up healing, he eventually went under the surgeon's knife in October.

His rehabilitation has been a slow process, with Preston taking a softly-softly approach to avoid a relapse.

The 24-year-old has patiently built up his strength and mobility over the summer while the rest of the squad have been on holiday.

But the club's medics are still not ready to throw him into full training just yet. The situation with Nicholls seems similar, with a July 1 start coming just a little too soon.

He too had to sit out the start of pre-season, having treatment on a knee problem.

"He's doing well," explained Irvine. "He's got a little bit of a problem just now. But I don't think it's anything major from what the medical people tell me.

"Kevin has had his problems since I came here. He was in the team when I arrived, but then he picked up a couple of injuries so it's been quite frustrating for him.

"But hopefully he will be okay soon and joining in with the rest of the lads."

Nicholls spent last summer playing catch-up with the North End squad after signing from Leeds just weeks after undergoing knee surgery.

His first season at the club was not a happy one with the 29-year-old handing back the captain's armband only three months after being given it as Graham Alexander's successor.

Loss of form led to fans barracking the ex-Luton skipper and he played only four games after Irvine took charge.