The 27-year-old was an unused substitute during last Sunday's Carling Cup final defeat to Manchester United and has failed to secure a first-team spot at Villa Park since his £5million move from Chelsea in the summer of 2008.
But he is still afforded hero status at Reading where he scored 30 goals from midfield in a four-year spell before leaving to join Jose Mourinho's Chelsea on a free transfer.
McDermott said: "Steve Sidwell could well start and everyone at Reading will only speak highly of him.
"He left the club on a Bosman but his attitude that season was first class.
"He was always available for selection and never pulled out of any tackles. He was 100% committed in every game up until the day he left and we look forward to seeing him on Sunday."
Sidwell could come up against Reading midfielder Jay Tabb in the centre of the pitch and the former Brentford and Coventry man has admitted a win and a place in the last four would be a dream come true.
McDermott's side have vastly improved since beating Liverpool in round three in January and will approach the tie full of confidence.
Tabb said: "This is a great tie for us against a Villa team looking at a top-four finish in the best league in the world.
"The cup has been a turning point for us this season and I've always loved the FA Cup.
"It's a great competition and I'm really looking forward to playing on Sunday.
"The further you go, the more people sit up and take notice.
"We are top of the form table at the moment and we have already beaten big teams to get this far so we have no fear.
"It is a great achievement from the squad to get this far and we want to keep it going.
"The chance to play at Wembley hasn't sunk in yet but we will give it everything to get through to the semi-final."
Aston Villa 5/6, Draw 12/5, Reading 10/3