The Reading boss has quelled rumours that he is punishing the Republic of Ireland international for not agreeing to a new contract at the club
The 24-year-old centre back, whose contract runs out at the end of the season, has fallen behind Sean Morrison in the pecking order at the Madejski Stadium and McDermott has stressed that it is 'just a personnel decision'.
"Obviously I'm frustrated with the contract situation, it's a good offer, he's got to make his mind up," McDermott said. "He says he wants to stay and play for me, he has to make his own mind up on that."
He continued: "I thought Morrison was excellent against United and it was just a personnel decision. You live and die by that.
"I spoke to Pearcey on Friday, I said to him he needs to do better (for both goals against Stoke)," added the Reading boss.
"He had to do better picking up Robert Huth for the set play and then when (Cameron) Jerome turned him for the second goal. He accepted that."
Meanwhile, Sunderland winger James McClean has been forced to close his Twitter account by club officials after a politician objected to a tweet referring to a song by the band The Wolfe Tones.
Gregory Campbell of the Democratic Unionist Party (DUP) criticised the former Derry City player for promoting a song which he said was 'openly pro-IRA'.
McClean expressed his enjoyment of the song 'Broad Black Brimmer', a song which is centred around the context of the Irish War of Independence and the Irish Civil War of the early 20th century.
Other Ireland internationals, including Hull City midfielder David Meyler and Toronto defender Darren O'Dea also expressed their enjoyment of the song.