Robinson said: "Alex played really, really well aganst Fiji.Those three or four early tackles he put in showed he has superb timing and that he has got a good head on strong shoulders.
He added: "We are giving the players the opportunity to perform against the Wallabies, who are a top quality international side - the sort that everyone wants to test themselves against.
"Competition for places is intense and we'll be watching the Scotland A game against Tonga in Gala on Friday night very closely.
"But we are saying to the players for Saturday step up this weekend and show improvement."
The players selected in the Scotland squad have some 611 caps between them and have scored 1012 points in international rugby.
Scotland team (sponsor Murray) to play Australia in the Bank of Scotland Corporate Autumn Test on Saturday 21 November at Murrayfield (kick-off 5.15pm):
15 Rory Lamont (Toulon)
14 Sean Lamont (Scarlets)
13 Alex Grove (Worcester Warriors)
12 Graeme Morrison (Glasgow Warriors)
11 Simon Danielli (Ulster)
10 Phil Godman (Edinburgh)
9 Chris Cusiter (Glasgow Warriors) CAPTAIN
1 Allan Jacobsen (Edinburgh)
2 Ross Ford (Edinburgh)
3 Moray Low (Glasgow Warriors)
4 Nathan Hines (Leinster)
5 Alastair Kellock (Glasgow Warriors)
6 Alasdair Strokosch (Gloucester)
8 Johnnie Beattie (Glasgow Warriors)
7 John Barclay (Glasgow Warriors)
16 Dougie Hall (Glasgow Warriors)
17 Kyle Traynor (Edinburgh)
18 Jason White (Clermont Auvergne)
19 Richie Vernon (Glasgow Warriors)
20 Mike Blair (Edinburgh)
21 Chris Paterson (Edinburgh)
22 Nick De Luca (Edinburgh)