Goals from Lucas Joao and George Puscas were not enough for Veljko Paunovic's side to stay unbeaten as the hosts claimed their second win of the season.
However they still remain three points clear at the top of the Championship.
Meanwhile Alex Neil's Preston North End sit 16th after losing all of their home matches but remaining unbeaten away from home.
Last time out they lost 1-2 to Birmingham City at Deepdale.
Reading remain without key stars John Swift and Andy Yiadom.
Yakou Meite was injured in the side's win against Blackburn Rovers last week, missing Friday's clash with Coventry, and is expected to remain sidelined for this clash.
Ovie Ejaria is in contention to be recalled after a muscle fatigue ruled him out of the previous two games.
Liam Moore is a doubt after being substitued at St. Andrews through injury.
For the visitors, Ben Davies and Scott Sinclair are expected to be recalled.
Reading possible starting lineup:
Cabral; Esteves, Morrison, Moore, Richards; Rinomhota, Laurent; Meite, Semedo, Olise; Joao.
Preston North End possible starting lineup:
Rudd; Fisher, Bauer, Davies, Hughes; Browne, Ledson; Sinclair, Johnson, Potts; Jakobsen.
Ones to watch
Joao continued his hot run of form by notching the first against Coventry City.
He has now scored six in nine league matches, more than he scored during the whole 2019/20 campaign.
Youngster Michael Olise is also in a rich vein of form, with two goals and three assists for the 18-year-old.
Experienced Sinclair is the Lancashire club's top scorer with four.
He is someone Royals fans know well after his hattrick for Swansea City in the 2010/11 Championship Play-Off Final.
Last season Reading did the double over Preston, with a 1-0 home win in Mark Bowen's first match in charge and an impressive 2-0 win at Deepdale between Christmas and the New Year.
Neil's side last beat Reading in 2017, a run stretching back five matches.
Serbian Paunovic is disappointed in the key injuries his side are picking up, but insists his side must keep improving and picking up results.
"We will always keep ourselves accountable for our performances.
“We have to be ready for Wednesday night. We have to do a good job of recovering from fatigue and knocks ourselves – the players’ mindset and bodies have to be in the best possible shape.
“What hurts me is seeing our players getting hurt and missing games, missing the opportunities to perform and play football. We don’t control injuries though, we can only control our attitude and how we respond to our busy schedule. We have to keep improving, recovering and keep everyone connected.
“And it is important that everyone stays engaged. Because if an injury does happen, then the next man has to step up.”
Former Norwich City manager Neil insists Reading have managed to find the right balance so far this season and the first goal will be vital.
“They have always had a good group of individuals and what they have managed to do this is, is to structure that in a way that has allowed them to go and show what they can do.
“That has probably been an issue for them over the last couple of seasons, but, as we saw in the last game that they played, they do concede goals and Coventry managed to beat them.
“Blackburn totally dominated the ball. Reading started really well; got the goals they needed and then were happy to sit in their shape and hit them in transition.
“The first goal is going to be important – as it always is – and we just need to make sure we start the game well and do what we have been doing away from home."
How to Watch
The game is not on Sky Sports and so is exclusively available on iFollow for £10, just £7 if you are watching from outside the UK.