The Lions' next opponents scored 11 tries in a 67-5 success in Wellington but now face a midfield crisis after losing centres Rob Horne, Pat McCabe and Anthony Faingaa.
Horne suffered a fractured cheekbone early on in the Cake Tin and was forced out of the game eight minutes into the second half, while McCabe dislocated his shoulder and had to be replaced by hooker Stephen Moore after the Wallabies ran out of backline subs.
Fainagaa was then knocked out by a knee to the head while making a tackle in the final minute and was carried off on a stretcher after receiving extensive on-field treatment.
Australia also lost No8 Wycliff Palu to a hamstring problem, while full back Kurtley Beale was replaced at the end of the first period after complaining that he was 'tightening up'.
Deans will now wait for the official diagnosis of the damage to all five players before deciding whether to call up any replacements to his 30-man squad.
"It's pretty extensive," said a pragmatic Deans.
"We may have to (call up replacements). But we'll see what the medics say before we make that sort of decision.
"It's part of the game. Obviously it would be better to avoid them but that's how it happens."
Injuries aside, Deans was more than happy with his team's performance as they put their 15-6 reverse to the Irish behind them in the best possible fashion.
The 1991 and 1999 World Cup winners had a bonus point sewn up before half time thanks to scores from Horne, Rocky Elsom, Beale and Faingaa.
The newly-crowned Tri Nations Champions were even more impressive after the break as they crossed the American line a further seven times.
Ashley-Cooper stole the headlines with three of those tries in a sensational seven-minute period, with Drew Mitchell, McCabe, Faingaa and Radike Samo also touching down in New Zealand's capital.
"We were pleased (with the result). It wasn't perfect, but there are elements in that game which we made good progress on," added Deans.
"They maintained their momentum and approached the game with a slightly better mentality, with a bit more discipline in their decisions.
"The pack didn't chase the rainbow, they adjusted their approach and as a result put the pressure on. We got the ball in and applied the pressure."
Australia finish their Pool C campaign with a clash with Russia on October 1 before facing a likely quarter-final against reigning world kings South Africa.