The 20-year-old former Southampton starlet had been limited to just 54 minutes of action in 2009/10 through injury.
And he is now set to endure another month on the sidelines after a robust challenge from Birmingham City defender Liam Ridgwell at the weekend left him with knee ligament damage.
Walcott is vying for the most competitive position in Fabio Capello's squad ahead of next year's global showpiece - right midfield - with David Beckham, Shaun Wright-Phillips, Aaron Lennon and James Milner all in contention.
And the youngster's club manager has confessed that Walcott is concerned that his constant lack of fitness is seeing him drop further down the pecking order.
"Theo is worried about the World Cup certainly, but I don't think there’s any reason to worry now," he said.
"He will be in the squad. He will be fit. It's October and he has an injury of two to three weeks. I say four to be covered.
"I don't think he is fragile, not really. I have not completely made my mind up.
"He's had two shoulder surgeries that were a genetical weakness, from the family. From the rest, I don't believe he is injury prone.
"Don't forget usually it is the striker who gets hit and the defender who hits. Most of the time the strikers are more injury prone because of the way the game is played. The quicker they are the more they get kicked and at a higher pace."
