The midfielder was dropped from the starting lineup for Saturday's 3-3 draw with Fulham, prompting speculation that there had been a bust-up between the manager and his player.
However, McDermott is adamant that there have been no disputes between the pair.
"There's no bust-up," said McDermott. "He wasn't selected to play for the game.
"So, I don't know where the reports are coming from. Danny was training yesterday."
Guthrie joined the Royals in the summer from Newcastle United.