Walcott was one of a number of Gunners players to be struck down by a virus in Shanghai earlier this week and subsequently only played 45 minutes of a penalty shootout victory over Bayern Munich. Olivier Giroud, Per Mertesacker and Aaron Ramsey were also affected, while new signing Sead Kolasinac was sick on the pitch before being replaced.
Providing an update on that situation during a brief press conference held on Friday, manager Arsene Wenger revealed that most of his players were now fit but that Walcott remained doubtful for an all-Premier League affair at the Bird's Nest.
"Theo might not play," he said. "Today we had 21 players fit. Theo was not ready to train and I don't think he will be ready, but it's nothing major."
Wenger initially attributed that illness being passed around the camp to food poisoning, although The Mail reported on Thursday that Arsenal medics believed it was more likely to be a mild stomach bug.
While Mertesacker played no part against Bayern due to illness, defensive colleague Koscielny missed the match due to a back problem. Such a shortfall left Wenger having to deploy midfielder and reported Leicester City target Mohamed Elneny as a makeshift centre-back.
Appearing alongside Wenger in front of the media in the Chinese capital, Koscielny claimed the issue was improving but that he would need to assess it again before the match.
"It is better, I had a little pain Tuesday morning," he was quoted as saying by football.london. "Today I trained, it's okay, not 100 per cent. I will see tomorrow."
This weekend's clash between Arsenal and Chelsea is the fourth meeting of the two clubs in as many months, with the pair having gone head-to-head in the FA Cup final in May. They are also due to square off at Wembley in the Community Shield next month and will meet in the Premier League at Stamford Bridge on 17 September.
Despite this latest meeting only being a friendly, Wenger is still expecting a tough test against the reigning top-flight champions.
"It's always difficult to predict, but [although] it's a friendly between Chelsea and Arsenal, it's not really a friendly because there's always some pride at stake and some London desire to have the superiority," he added.
"It was a very interesting game in the final of the FA Cup, and we play against Chelsea in the Community Shield, and again very early in the season. We know each other very well and it's difficult to know how prepared Chelsea are and how far we are with our preparations. Saturday will be a good indication of that and we were good against Bayern. This is another test for us before the season."