The midfielder has not featured for the Royals since the 1-0 defeat at Liverpool in October, and is believed to have reprimanded by the club for not making the trip to the Stadium of Light.
The Royals crashed to a 3-0 defeat on Wearside, their fourth loss on the bounce which leaves them 19th in the table and six points off safety.
Royals boss Brian McDermott confirmed afterwards that Guthrie had refused to travel and is planning on holding talks with the 25-year-old.
"He made a decision that his head wasn't right to travel," McDermott said.
"Everyone has got to be going in the same direction, that's really, really important for me as a group, and we have had that for a period of time.
"You have to put yourself up to be selected in each and every game, and that means every player.
"Any player has to be part of what we are about. We can't deviate from what we have been about over the last three years.
"We are very much about the group - we have to be. We all have to pull in the same direction. It's probably not a conversation for this evening, but it's something that we need to address in the week."