Along with young striker Brian Madjo and fellow defender Modou Cisse, Harwood-Bellis was left out for Europe by Emery as the head coach failed to find room.
It has happened before, with Donyell Malen and Andres Garcia last season – Malen eventually left for Roma last January as he looked for more playing time and responsibility.
Emery is banking on the flexibility of Lamare Bogarde and Boubacar Kamara to fill in at the back if his defence is stretched, although that will be of little comfort to Harwood-Bellis.
“Because in Europe you can have 23 players and in the league not,” Emery said. “[Mikel] Arteta wanted to open it for more players. We needed to take off someone, and it was Taylor.
“It is hard, the decision we took, and for the players. The experience we have here, when we were without Malen, Andres. To decide, it is through the analysis of how we are expecting to be until January.
“We are going to play eight matches. Cisse is not in because he is injured. Madjo is still injured for the next two weeks minimum. Taylor arrived as the last one, and we can get the balance with Lamare Bogarde, and we can even play Kamara.
“We tried to analyse it deeply. Taylor will be here for a long time, and hopefully, we will have the opportunity to play in Europe with us, in January maybe, and the next few years.”