Jamie Macmillan says his recent hamstring setback came as a complete surprise, with no signs or symptoms in the lead-up to the injury.

The 23-year-old suffered a low-grade right hamstring tear in the final quarter of North's win over Essendon in round 16 and is expected to be sidelined for another fortnight.

Macmillan said both he and the club's medical team remained "puzzled" by how he tweaked his hamstring for the first time in his career.

"I didn't have any soreness or anything in between before it actually happened," Macmillan told SEN's Evenings with Finey on Monday night.

"I was going to take off to run and it went ping and the physio did message (me) later that night when I was up icing it and he said, 'If you can think of anything that's caused it, please let me know'.

"And I said, 'The last time I did a soft tissue injury was in Boomer's 299th game and the one I did it in was in his 399th game' and that's about the only thing I could think of."

Macmillan said club medicos initially feared he had suffered a more serious hamstring injury similar to the one that saw midfielder Nick Dal Santo miss 10 weeks earlier this season.

"They were pretty worried initially but scans the following day just showed (a tear to) the belly of the muscle," he said.

"They're reluctant to use the term 'tear' these days, but for us non-medicos it's just a small tear.

"Twenty-one days is the earliest you can get back."

Injury List: Round 18