Reigning IRB world player of the year Brodie Retallick has been ruled out of Super Rugby for a month with a shoulder injury in a major blow to the Chiefs.

Retallick has injured his left shoulder and his place in Saturday’s night’s clash with the Melbourne Rebels at AAMI Stadium will be taken by Michael Fitzgerald.

The 23-year-old Retallick injured his right shoulder earlier in the season for the Chiefs who are one point behind New Zealand conference leaders the Hurricanes.

All Black Retallick is one of six changes to the Chiefs’ starting team with coach Dave Rennie opting for Andrew Horrell at five-eighth.

Horrell takes over from Marty McKenzie, who got first go in the No.10 jersey in the 35-27 win over the Western Force last Friday after All Black Aaron Cruden’s season-ending knee injury.

McKenzie has missed out on the 23 for the clash with the Rebels with younger brother Damian McKenzie retaining his spot in the reserves as back-up No.10.

Skipper Liam Messam returns as blindside flanker after a week off under the All Blacks rest program.

There are changes to both propping positions, with tighthead Ben Tameifuna and Pauliasi Manu in for Siate Tokolahi and Mitchell Graham.

James Lowe comes back at left wing, with Tim Nanai-Williams moving to the right and Bryce Heem dropping to bench.

The Chiefs are fourth on the overall table, but are just one point behind competition leaders the Hurricanes in the New Zealand conference.

The Rebels, who were pipped by defending champions the Waratahs 18-16 last weekend, are 11th, eight points outside the top six.

Chiefs: Tom Marshall, Tim Nanai-Williams, Charlie Ngatai, Sonny Bill Williams, James Lowe, Andrew Horrell, Brad Weber, Michael Leitch, Sam Cane, Liam Messam (capt), Michael Fitzgerald, Matt Symons, Ben Tameifuna, Hika Elliot, Pauliasi Manu. Res: Quentin MacDonald, Siate Tokolahi, Jamie Mackintosh, Michael Allardice, Johan Bardoul, Augustine Pulu, Damian McKenzie, Bryce Heem.