According to The Telegraph's Sam Dean, Guendouzi got into a "heated row" with the Spaniard and the coaching staff during their warm-weather training camp in Dubai.
It's said the clash started in training and continued at the team hotel.
Per Dean, after the win against Newcastle, Arteta said the player's behaviour and work in training were the reasons he was dropped:
The 20-year-old has been a regular fixture and a key part of Arsenal's midfield for the Gunners since his arrival from FC Lorient in 2018:
An all-action presence in the centre, he often drives the team forwards, and he puts in plenty of defensive work, too.
His performances and development have somewhat stalled of late, though.
Reach PLC football editor Tom Marshall-Bailey and TalkSport's Matt Scott were critical of his performance in Arsenal's 0-0 draw with Burnley prior to the winter break:
Football.London's James Benge is a huge admirer of the youngster, though:
His replacement against Newcastle, Dani Ceballos, made his first Premier League appearance since November.
The midfielder impressed with an influential showing against the Magpies, particularly in the second half as Arsenal blew their opponents away with goals from Pierre-Emerick Aubameyang, Nicolas Pepe, Mesut Ozil and Alexandre Lacazette.
Ceballos' performance warrants a run in the side in the coming weeks, so Guendouzi may be set for a spell out of the team, but the youngster could benefit long-term from having the competition.