WHILE most of his teammates push through two-hour training sessions, North Melbourne key forward prospect Nathan O'Keefe can struggle to find the energy for just a handful of drills.

Such is the lingering effect of glandular fever, which has robbed O'Keefe of his fitness after what had been such a promising start to his pre-season.

The 19-year-old discovered he had the virus in mid-December and sat out more than three weeks of the summer program, including last month's training camp on the Gold Coast.

He has since regained four of the five kilograms he lost through his illness, but still has some ground to make.

"After any sort of work I just feel lethargic," O'Keefe said. "I don't have a lot of energy to do much after I've done an exercise. It's knocked me around a bit.

"It's been pretty hard not training. All of the boys were obviously getting fit up at the Gold Coast. I'm getting back there slowly."

Club doctor Con Mitropoulos has carefully monitored O'Keefe's condition and has the youngster on a dose of antibiotics to help protect his immune system.

Involved in some light skill work ahead of last week's intra-club match in Ballarat, O'Keefe has managed to increase his training load to a point where he may be considered for Friday's second game.

However, it has been difficult to plan for his availability.

"It's a bit hard to know with glandular. Some days I wake up and feel good. Other days I just wake up without any energy at all," he said, adding that he should be able to return to a full program later this month.

Senior coach Brad Scott had told O'Keefe soon before Christmas that he was pleased with his continued development, which saw him elevated from VFL affiliate Werribee's reserves to its senior side for four games in July and August.

Selected from Eastern Ranges with North's fourth-round pick (No.59 overall) in the 2008 NAB AFL Draft, O'Keefe was considered a long-term project by the club.

Since his arrival at Arden Street, he has added almost 10 kilograms to his slight frame.

"When I came to North, it was a rare case ... I had only played seven TAC Cup games before that," he said.

"It's a long track but my main focus at this stage is to get all the development things right, build my body up, put weight on and stuff like that. That's all coming along now."