Metcalfe has a back strain, and Henderson is unavailable after suffering a blow to the head against Sale Sharks at Heywood Road last week in Round 5.
In all their are eight changes, including three positional switches, to the squad that suffered the 45-3 reverse against the Sharks last weekend.
Stuart Moffat has switched to full back to replace Metcalfe, with Michael Bartlett returning on the left wing. It will be Bartlett's first start since the Bank of Scotland Pro Rugby Cup match against Edinburgh on 1 November. Tommy Hayes has moved out to inside centre in place of Henderson, with Calvin Howarth at outside-half. David Hilton has transferred to tight head to replace Harrison, with Cameron Blades recalled as left prop.
Elsewhere in the pack, Nathan Ross and Gordon Simpson are in respectively at lock and No.8, with Andy Hall and Jon Petrie switched to the substitutes' bench. Prop Lee Harrison is unavailable as ligaments in his right knee were damaged in training.