"He is a bit unlucky not to score a couple of extra goals. But that one today will give him unbelievable confidence," added the Scot, who turned 69 on New Year's Eve.
"Hopefully he kicks on from there."
Ferguson believes Rooney's ankle "will be OK" but the Scot added that he remained concerned about other players who picked up injuries.
"Wayne had to come off for a spell, Patrice Evra went down injured, Darron Gibson got an injury to his groin. We were struggling in the last 10 to 15 minutes in terms of not having 11 fully fit players on the pitch," he said on the club website.
Meanwhile, Ferguson believed his veteran full-back Gary Neville should have been sent off for appearing to pull down West Brom's Graham Dorrans in the 18-yard area during the first half.
Phelan admits Man Utd were 'lucky'
"Gary was lucky to stay on," added Ferguson, who was fortunate to see referee Chris Foy wave play on.
"It was a penalty. At first I thought he had got a touch but when I saw it again, he was lucky."
West Brom manager Roberto di Matteo, perhaps predictably, also agreed with Ferguson's belief that Neville should not have stayed on the pitch.
"I feel frustrated. There was an incident in the first half where a United player [Neville] should have been sent off and we should have got a penalty," said the Italian.
Neville should have been shown red - Di Matteo
"Of course I can't just point to that one moment because we've made our own mistakes."
One of those was a penalty missed by striker Peter Odemwingie with the score at 1-1. The Nigerian fired his effort wide of former Baggies keeper Tomasz Kuszczak's right-hand post.
"We were awarded a penalty and we missed it. In the Premier League, if you don't take those chances then you'll be in danger of losing," said Di Matteo.
"We are doing a lot of work and not getting any reward. We need to improve and we will try to make it better. I can't blame my players for this because the commitment is there."
This page is best viewed in an up-to-date web browser with style sheets (CSS) enabled. While you will be able to view the content of this page in your current browser, you will not be able to get the full visual experience. Please consider upgrading your browser software or enabling style sheets (CSS) if you are able to do so.