The 23-year-old Gunners forward was forced out of the Three Lions' 5-0 World Cup 2014 Group H qualification clash after just 10 minutes following an early collision with the San Marino goalkeeper Aldo Simoncini.
Walcott was treated on the Wembley pitch for several minutes before being helped off and then taken to hospital for a scan on his chest.
As a result, Walcott is not only a doubt for England's second qualifier against Poland in Warsaw on Tuesday, but he could also miss Arsenal's Premier League clash with Norwich City at Carrow Road next Saturday evening.
It was a good night Walcott's Arsenal team-mate Alex Oxlade-Chamberlain as he grabbed England's fifth goal to not only score his first international goal, but also become his country's fourth youngest scorer behind Wayne Rooney, Michael Owen and Tommy Lawton.
Oxlade-Chamberlain, whose father Mark Chamberlain was a former England international, said afterwards: "It's a relief to get the monkey off my back, as they say. I have been looking for my first goal for England and my dad's been pushing me, telling me I needed a goal."