Beyond the tactical headache, Arteta confirmed that the substitution of Calafiori was also enforced.
The Italian defender was replaced by Mosquera at half-time, leaving Arsenal with a makeshift backline for much of the second period at the London Stadium.
"Richy [Calafiori] felt something and we couldn't take the risk," Arteta revealed. With Ben White’s knee injury described as "not looking good", the Arsenal boss is facing a potential defensive selection crisis at the worst possible time.
"We are thin in those positions now, but the attitude and the courage of the players who stepped in-especially Mosquera and [Myles] Lewis-Skelly-was outstanding under huge pressure," he said.