However, this double blow is partially softened by the recall of the former Scotland A stand-off, Stuart Laing. He has impressed this season with his goalkicking while playing as a stand-in for Humphreys. Gary Longwell, a seasoned veteran, returns to the second row in place of Davidson and will partner the Irish international Paddy Johns, who has been released by Saracens.
Ulster can call on four other capped players as well as Johns- the centres Mark McCall and Maurice Field, Denis McBride, who at flanker will captain Ulster, and the right wing James Topping, who made his Ireland debut in the shock defeat by Western Samoa on Tuesday night.
Saracens, in the guise of Michael Lynagh's XV, field six internationals for their match against the touring Australian side Queensland at Enfield on Sunday. Lynagh, who was capped 72 times from Queensland and scored a world record 911 points, will lead the Londoners when they face his former state side. Philippe Sella, Kyran Bracken, Tony Daly, Paul Wallace and Tony Copsey are also on parade for a game the Saracens coaching director, Mark Evans, views as extremely important.
"When you play a team as good as Queensland, the least you owe them is to put out the strongest available side. It would have been an insult for us to do otherwise," Evans said. "This is possibly the last opportunity for our guys to play together before we get back to league and cup matters."
Queensland's British tour includes fixtures with English divisional sides, concluding on 13 December against England A.
France's Patrick Thomas will referee the Heineken European Cup quarter- final between Dax and Toulouse at Parc Municipal des Sports on Saturday. The official, who was in charge of last Saturday's international between Scotland and Australia at Murrayfield, will make it an all-French affair as Toulouse continue their defence of the trophy.
The Welsh referee Clayton Thomas will control the all-England contest between Leicester and Harlequins at Welford Road, with the Irishman Gordon Black officiating the Anglo-Welsh game between Cardiff and Bath at Cardiff Arms Park.
England's Brian Campsall will be in charge for Sunday's quarter-final at Brive, where Llanelli will be bidding to take the French club's 100 per cent record in the tournament and claim a place in the last four. Brive are the bookmakers' favourites to win the cup.
The BBC have altered the running order of Grandstand on Saturday to include live rugby union with second-half coverage of Leicester v Harlequins quarter- final at 3.45.
ULSTER (v Australia, Saturday): R Morrow; J Topping, M Field, M McCall, J Cummingham; S Laing, S Matchett; R Mackey, S Ritchie, G Leslie, G Longwell, P Johns, S Duncan, S McKinty, D McBride (capt). Replacements: R Irwin, A Adair, J Patterson, R Wilson, N McCluskey, N Doak.Reuse content