Coach Roberto Di Matteo said he expected a stern challenge from the visitors to Stamford Bridge for a match re-arranged because Chelsea face Europa League winners Atletico Madrid in the European Super Cup match in Monaco next week.
Reading, back in the top flight after four seasons in the Championship, drew 1-1 at home to Stoke on Saturday and Di Matteo said he would not be taking them lightly.
"I'm very wary of newly promoted teams like Reading and Southampton," he told a news conference on Tuesday.
"It's a very difficult game when you play a newly promoted team early on, full of enthusiasm and spirit. You sometimes look at it and think you don't want to change a winning team but it doesn't always work like that.
"Ramires is fine, [Marko] Marin is still out, so apart from his hamstring injury we are OK. It won't be long, but it might not be before the international break, we will have to see.
Di Matteo said Chelsea were looking to integrate Brazil midfielder Oscar gradually into their squad. "He hasn't been with us long so we have to give him the right time to get used to his new team-mates, the club and the team, do some tactical work with him and slowly put him into the team."
"He has done a wonderful job. They had a great run in the second half of the season. I followed the Championship a lot and they're difficult to play against.
"They don't concede many goals and are a threat on the counter-attack. I always found it hard to play against Brian McDermott's teams."
