The 28-year-old player is out of contract this summer and has failed to secure a regular spot in the Royals' matchday squad this season.
Tabb, who has made 16 appearances for Reading this season, is likely to find his first-team opportunities further limited following the arrival of Hope Akpan and Daniel Carrico during this transfer window.
McDermott told the official Reading website: "I spoke to Jay, he is a fantastic person and I need to do right by him. I said to him 'if an opportunity comes your way that is right and the clubs do a deal, I will not stand in your way'.
"Make no mistake, I rate him very highly. At this moment in time he's not been offered a contract so I'm trying to do right by him, it's a fine balance.
"We've signed Hope and Daniel, we have five or six midfield players, if he's not in our 18 every week and if he wants to go and play I'll do right by him."
Tabb added: "I've played 12 or 13 games this season and done pretty well, obviously the club signed two more midfielders and without a new contract offer it was kind of expected, the writing was on the wall.
"Of course I wanted to stay but you can't force clubs to keep you. I'm sure if I move in January the club will wish me well and I will wish the club well. The fans have been great to me, the same with the players as well, and if I'm needed before the end of the season they can rely on me."