The 28-year-old has made 12 Barclays Premier League appearances this season, his last start coming in the defeat at Manchester City on December 22. However, McDermott has just signed Hope Akpan from Crawley and Sporting Lisbon captain Daniel Carrico and now views Tabb's position further down the pecking order.
"Jay Tabb is a fantastic person and I need to do right by him," McDermott told BBC Radio Berkshire.
"The last thing I want to happen with Jay is to come to the end of the summer and he is stuck in a queue with a lot of other players.
"I've spoken to him and I've said if the right opportunity comes your way that you think is right and the clubs do a deal, then I will not stand in your way.
"I rate him very highly but at this moment in time he has not been offered a contract.
"It is a balancing act.
"We have just signed Hope Akpan and Daniel Carrico and have five or six top midfield players and if Jay wants to play elsewhere then I will do right by him."