England skipper David Beckham suffered a hairline fracture to one of his ribs during England's 2-0 win over Wales at Old Trafford, X-rays revealed late on Saturday.
An FA spokeswoman confirmed that a second set of X-rays revealed the extent of the injury after an earlier set appeared to give him the all-clear.
But it was not immediately clear how long the injury would sideline him for.
Beckham had an afternoon to remember back at Old Trafford where he spent more than a decade of his career with Manchester United.
He scored a spectacular goal after 76 minutes to secure England's victory, then got himself booked and suspended for their next qualifier in Baku against Azerbaijan on Wednesday.
After the match England coach Sven-Goran Eriksson praised Beckham for his goal rather than scolded him for a pointless yellow card which earned him his suspension.
Asked if he thought the booking irresponsible, Eriksson told a news conference: "No. I don't think so. Let's talk about the goal he scored instead, because that was an important goal.
"As long as it's 1-0, even if you create chances, you are never calm on the bench. 2-0 killed the game. We told the players at halftime we needed a second goal...and it came."
Eriksson said that striker Michael Owen, who has deputised for Beckham in the past, would probably wear the skipper's armband on Wednesday.
Impressed by Owen's lively performance after a difficult start to his Real Madrid career, Eriksson said: "I don't know if he'll be credited with the first goal or not, but I think he played very well.
"I haven't seen him that bright for a long time. It's good for him, good for England and probably for Real Madrid as well."
It was a bitter day though for outgoing Wales boss Mark Hughes, who had scored the only goal of the game on his international debut when these teams last met 20 years ago in Wrexham.
"We're disappointed. We'd hoped it was going to be a good day for us," the former United striker said on his return to Old Trafford.
"There were contributing factors, we lost Andy Melville minutes before the kickoff, so that disrupted us. In that initial 20-minute period, when you hope to be nice and solid, that was too disruptive for us and we conceded a deflected goal.
"At that point, it would have been very easy to go under but, fair play to the players, they dug in. In the second half, I just felt we'd got a foothold in the game and England scored a great goal."