Aguero, who had earlier saw Kevin De Bruyne fluff his lines from the spot, has now missed four of his own this term for club and country, which Koeman believes could be down to some sort of mental block.
"To miss two penalties, maybe it is a little bit of a mental question," he told reporters. "Maybe for Aguero. I don't know, because it's not the first time that he's missed."
Aguero has scored 11 goals in nine appearances for City in all competitions this season, but none in his last three outings.