The Chiefs are set to lose All Blacks stars Liam Messam and Sonny Bill Williams to sevens next season which, in addition to a cleanout of outside backs and locks, has left a gaping hole to fill in the franchise's 2016 Super Rugby roster.

Chiefs head coach Dave Rennie confirmed his captain Messam was going to focus totally on sevens next year in a bid to make the New Zealand team for the Rio Olympic Games, while it's looking likely that Williams will join him.

Rennie said Messam's confirmed departure left a massive void in the squad.

"Not just his playing ability but his leadership - he's very charismatic, incredibly passionate - he'll be very difficult to replace."

Messam will need to reduce his weight-muscle mass from 15-a-side loose forward in order to play sevens and needs to concentrate exclusively on the Olympic code.

"But it's exciting for him. He obviously won a gold medal at Commonwealth Games and to try and win an Olympic gold would be pretty special so we'll fully support it and who knows, he may be back in '17."

In addition to Messam and Williams, who were both named in the All Blacks' 41-man squad on Sunday along with fellow Chiefs Hika Elliot, Brodie Retallick, Sam Cane and Tawera Kerr-Barlow, up to nine other players could be leaving.

James Lowe, who is contracted for two more years, is the only remaining outside back with Tom Marshall going to England (Gloucester), Hosea Gear to France (Clermont), Bryce Heem to England (Worcester) and Tim Nanai-Williams to Japan.

Add midfield back Williams to that list and with first-five Marty McKenzie a possible defector to the Crusaders, that leaves a large number of backs to be replaced.

In the forwards the Chiefs are hit hardest at lock where the hard working pair of Matt Symons (London Irish) and Mike FitzGerald (Leicester) are leaving for English playing contracts, while Messam and young tighthead prop Ben Tameifuna (Racing Metro, France) add exponentially to the talent drain from the franchise.

With Bay of Plenty and All Blacks hooker Nathan Harris due back from the serious ankle injury that ruled him out of the 2015 season, and the successful return of Hika Elliot from his neck injury this year, there will be one hooker surplus to requirements next season with both Rhys Marshall and Quentin MacDonald coming off contract.

"There are still a lot of spots open and wider training group spots of course, but there'll obviously be a fair few new faces coming in which is exciting," Rennie said.

"There might be 10 or 11 changes with guys getting other opportunities and so on, but that's pretty standard. We normally lose a quarter to a third of our side each year.

"More often than not it's been some of the older guys heading off later in their career but last year Bundee [Aki] left and Gareth Anscombe and guys like that who potentially could have played another six, seven or eight years in New Zealand so I suppose that trend is more common now and we're seeing the same thing with the likes of [Tameifuna] and Tom Marshall."

Rennie felt the talent was around to provide the replacements, but admitted it was thinner on the ground than even 12 months ago with overseas contracts the order of the day.

However, the ITM Cup throws up new talent every year and the Chiefs coaches will gear up to monitor seven matches every week during this season's competition.

Rennie does not give his side a pass mark for this season after they bowed out in the playoff qualifiers for the second year running, knocked out 24-14 by the Highlanders in Dunedin on Saturday night.

"Obviously we're happy to be part of the playoffs but the goal was to win a championship so to tip out in the quarters is bloody disappointing and not the way we wanted to send off all the guys who are leaving," Rennie said.

The Chiefs refuse to use their injuries as an excuse for the disappointing season despite nine players on the sidelines long term, including star All Blacks first-five Aaron Cruden. Their poor end to the year, losing five of their last seven matches, proved particularly costly.

"Certainly in the first half of the season we were really strong, we played a lot of good footy and we were really clinical and I think the balance we had was really good, but we lost our way a little bit and again last night we missed opportunities to move the ball to people in space," Rennie said.

"I think from an attack point of view we've been nowhere near as potent in the last couple of months.

"That's my responsibility so we need to look at that, while a big part of it is selection and while we've got quite a few guys already contracted we need to make sure we get the right sort of balance and pick players to play a certain style of footy so working out exactly what we need to do and who we need to do it with will be important in the next month or so."