He'll make his debut in the Warriors starting line-up to face Munster in the Celtic League on Saturday.
Warriors head coach Hugh Campbell said: "Spencer is a strong running, powerful, young centre with a good turn of pace and an ability to score tries. The second half of the Celtic League is crucial for us and we need to take every opportunity to work our way up the league table."
Spencer added: "I'm really looking forward to the new challenge of playing in the Celtic League. When you look at the main European competition, the Heineken Cup, it's the Celtic League teams that are performing really well, so I'm looking forward to going Ireland and Wales as well as facing the other Scottish teams and playing in some big games. The Warriors are a great bunch of lads and a talented side and it'll be good to take part in some exciting rugby."
He has been registered by Aberdeen GSFP and will turn out for the Warriors on permit as allowed by the Celtic League rules.
Six Warriors have been released from the Scotland 6 Nations squad for the match on Saturday – five starting (Rory Lamont, Graeme Morrison, Euan Murray, Craig Hamilton and captain Jon Petrie) and one on the bench (Scott Lawson). In addition, Colin Gregor starts at stand-off fresh from Scotland 7s duty at the IRB tournaments in Wellington and Los Angeles and Glasgow Hawks' scrum half Iain Monaghan, aka Snoopy, comes onto the bench to cover for the injured Graeme Beveridge who aggrivated a neck strain during training.
15 Rory Lamont
14 Hefin O'Hare
13 Graeme Morrison
12 Spencer Davey
11 Mike Roberts
10 Colin Gregor*
9 Sam Pinder
1 Kevin Tkachuk
2 Fergus Thomson*
3 Euan Murray*
4 Dan Turner
5 Craig Hamilton
6 Steve Swindall
7 Jon Petrie CAPTAIN
8 Gregor Hayter
SUBSTITUTES
16 Lee Harrison
17 Scott Lawson*
18 James Eddie
19 Stuart Corsar
20 Iain Monaghan
21 Iain Kennedy
22 Graydon Staniforth
* members of the Scottish Institute of Sport
Unavailable due to injury/illness: John Barclay (head), Tim Barker (knee), Scott Barrow (groin), John Beattie (glandular fever), Graeme Beveridge (neck), Calvin Howarth (ankle), Donnie Macfadyen (knee), Colin Shaw (knee), Andrew Wilson (ankle)