Boak has been chased by both Geelong and North Melbourne in recent months with media coverage of his contract negotiations reaching saturation point in July when Cats coach Chris Scott and star players Joel Selwood and Jimmy Bartel met with the 23-year-old in Adelaide.
North Melbourne also confirmed that coach Brad Scott and captain Andrew Swallow had made a detailed submission to Boak's manager, Tom Petroro.
Power football manager Peter Rohde recently revealed Boak wouldn't wait for the Power to sign a new coach before he signed and Cassisi said it was "promising" the club would have his signature this week.
"I think it's looking pretty promising from what I hear," Cassisi said.
"His leadership around the place, his professionalism, the way he trains, you can't really put a value on all the stuff he does away from game day so it'll be huge for the club."
Speaking at an Adelaide hotel after Sunday's final-round draw with Richmond, Cassisi said Boak's commitment to the club would mean a lot to its players as well as its supporter base.
"If we can re-sign Boak it's just great for our supporters to see that as a group we are united as players. No one wants to leave the place, we want to work hard together to get us back up," he said.
"By his actions that he's shown on a day to day basis, there's nothing to suggest that he's going to be leaving.
"We were in Melbourne yesterday and I saw him around his family. It’s a tough decision for him, he's really close to his mum and his sisters, as we all are with our families, but I'm really confident he's going to stay."
With Liam Jurrah's decision to quit Melbourne and move to Adelaide, the stage is set for the Power to acquire a host of new talent in the pre-season.
Rohde confirmed the Power had already been in touch with Jurrah's management about joining the club, but said it wanted to better understand the forward's "complicated issues" before deciding whether they would pursue him.
Regardless of what happens with Jurrah, the Power have previously said they would seek to improve their list through trade week and free agency.
Cassisi said if they could bring in two or three quality players and get a solid pre-season under their belt, the Power could improve rapidly in 2013.
"When you look at what Brad (Ebert) and John (McCarthy) have been able to bring to the group, I think maybe two or three more of them would really add to our depth and (increase) pressure for spots and all that sort of stuff," he said.
"[We'll] have a good eight weeks off, come back in good condition and have a great summer.
"Your season's often based around your summer, we've had 17 guys have operations [this year] which is not ideal, you can't shy away from that, but we need those guys to look after themselves and come back for a big pre-season."
Harry Thring is a reporter for AFL Media. Follow him on Twitter: @AFL_Harry.
