Downing, who signed from Middlesbrough in the summer, made his first appearance in a Villa shirt when he came off the bench against Burnley on the weekend after breaking a metatarsal in his foot when playing with Boro last season.
Downing was expected back a bit later than his November 21st return but O'Neill believes the prospects of making England's 23-man squad for South Africa have helped him recover more quickly.
"Of course the World Cup is a pretty big incentive," O'Neill said.
"He will definitely be thinking at the back of his mind that Capello may have him in his thoughts.
"He is so enthusiastic - one of the most enthusiastic trainers we have had and is desperate to get on.
"Anything the coaches ask him to do he will do and a bit more besides. He has been pretty extraordinary.
"I think, having played now even though it was just 20 minutes at Burnley, at least now he has been involved and he will be approaching these games with a wee bit more gusto."