The England international injured himself while training with his national side and needed help leaving the pitch before receiving treatment on his ankle. He missed the rest of the session, and Cross includes quotes from Roy Hodgson, who was briefly quizzed on the matter.
"Theo took a slight knock at the end of training, but we believe he’ll be okay. He’s very much still in contention."
Hodgson appears more relaxed about the situation, but this latest news will clearly come as a concern to Arsenal who are preparing to host Aston Villa this weekend.
With the Gunners failing to land a top-name striker this transfer window, much depends on Walcott replicating his consistent scoring form of last season, when he scored 14 Premier League goals.
Generally cutting in from the right, the England man was his club's top scorer, and Cross doubts whether Wenger would risk a semi-fit Walcott against Aston Villa.
His preseason form has been impressive thus far, which will frustrate Wenger further if he does indeed miss out. He was influential in a recent 3-1 win over Manchester City, scoring and producing the kind of display Arsenal fans have become increasingly familiar with.
Losing him now would throw a sizable spanner in the works of Arsene Wenger's preparation and would significantly boost Aston Villa's prospects for the weekend.
Walcott has often been troubled by injury throughout his career. A few years ago a recurrent shoulder issue saw him frequently sidelined, while he missed England games in March due to a pelvic muscle injury.
With competition for the Champions League places as intense as ever, Arsenal will hope one of their key men can brush off this latest niggle and be fit to face Villa.