Stirling Mortlock expects it all to come together much better for both his rebuilt back and the Melbourne Rebels over the next month.

So far the Rebels' three-week Super Rugby odyssey has had the lot - heavy defeat, stirring victory, then possession-starved loss to the previously win-less Chiefs in New Zealand last weekend.

Rebels skipper Mortlock says the uneven road so far will take time to smooth as the team gets used to the rigours of playing high-standard rugby together.

"The two losses - there has been a fair bit of time in both games where we've started okay, been in the game, then for one reason or another lost our way a bit," Mortlock told AAP.

"It's exacerbated by the fact that we haven't played a lot of rugby together.

"The more we get exposed to that sort of footy and the more we work on our systems, that will certainly be good for us.

"With a new team, it's something that takes a bit more time."

One bright spot has been Mortlock's return from back surgery - three competition matches plus two pre-season games in which the 33-year-old has shown he is fully healed.

But Mortlock admits getting back to peak form - especially recapturing what he calls "his top-end explosiveness" - is a work-in-progress.

"I really hope that probably the next month or so, my body will be as good as I'd like it to be, and hopefully I can have a bit more impact in the team," he added.

The Rebels clash with in-form South African side the Sharks at AAMI Park on Friday night.

They have moved to strengthen their lineout, which struggled badly against the Chiefs, with the return of former All Black Kevin O'Neill from a calf injury.

He replaces Adam Byrnes, who misses the squad altogether.

"Losing Kev (for the Chiefs match) was a significant loss and the reality was we were down in that area," Mortlock said.

"The lineout's such a tough thing to get together because there's so many moving parts.

"Kev's one of the best (in the lineouts) in our squad."

Injured trio Sam Cordingley, James Hilgendorf and Adam Freier are still not fit.

But league convert Luke Rooney earns a place on the bench after recovering from an abdominal injury.

Rebels: Mark Gerrard, Lachlan Mitchell, Stirling Mortlock (capt), Julian Huxley, Cooper Vuna, Danny Cipriani, Nick Phipps, Gareth Delve, Michael Lipman, Jarrod Saffy, Kevin O'Neill, Al Campbell, Greg Somerville, Ged Robinson, Nic Henderson. Res: Heath Tessmann, Laurie Weeks, Hugh Pyle, Tim Davidson, Richard Kingi, Afusipa Taumoepeau, Luke Rooney.

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