FOR the first time ever in an AFL game, Port Adelaide's captain on Sunday won't wear the No.1 guernsey.

But skipper Travis Boak's temporary switch to the No. 10 jumper he wore in his first six years at the Power is for a great cause.

Eight-year-old Henry Mickan, who suffers from leukaemia, will fulfill every Power supporter's dream when he leads the club out in the No.1 jumper onto Adelaide Oval for Sunday's game with Greater Western Sydney.

Boak is an ambassador for the Childhood Cancer Association and offered to hand over the captaincy to Henry for the day.

"The tradition that the club has had for a long time is for the captain to wear the No.1 guernsey – it's a great tradition and certainly an honour to wear that No.1 guernsey, and I have huge respect for it and have loved every minute of it," Boak told portadelaidefc.com.au.

"But for this weekend, it's a pretty special cause and it's all about Henry and his family and making sure we make it a special day for him.

"Part of that is for him to wear No.1 and for me to wear No.10, and I'm so proud of the club that we've been able to do this and I think the broader Port Adelaide community will understand that.

"We are so passionate about making our community proud and this is just one part of that."

The Power's captain has always worn the No.1 jumper since the club entered the AFL in 1997.

It has also been a long-standing tradition at Port Adelaide at state level, with Geof Motley in 1966 the last captain not to wear the No.1 jumper.