Nwaneri was an unused substitute in Sunday's 1-1 draw with Nice — a result that came despite Marseille being without three starting attackers through injury, making his omission all the more pointed.
Speaking to L1+, Beye offered no apology for the decision.
"He's a quality player, but he has to give us way more in his day-to-day commitment. Other players gave way more."
The relationship between manager and player carries additional baggage. Before Beye took the Marseille job in February, he managed Stade Rennais — and Nwaneri made a reckless challenge on Rennes midfielder Glen Kamara in a Coupe de France tie that kept Kamara sidelined for four games. Beye was furious at the time.
Under Roberto De Zerbi, who took Nwaneri to Marseille from Arsenal in January and has since moved to Tottenham Hotspur, the 19-year-old started four games and scored on his debut against Lens. Under Beye, he has not started a single match. He has played 412 minutes across his entire loan spell.
Beye had also offered a sharper assessment after a loss to Monaco earlier in the month.
"Ethan has great qualities, he's a great talent who needs to adapt to the intensity of Ligue 1. There are still aspects of his game that need to be much stronger in terms of counter-pressing, his defensive efforts to win the ball back."
Arsenal structured the loan deal with a clause that increases their financial return the less Nwaneri plays — meaning the club will profit financially from a spell that has not gone to plan on the pitch.
Chelsea and Borussia Dortmund are among the clubs understood to have interest in a permanent deal for Nwaneri in the summer. Arsenal are expected to assess his future once the loan concludes.