Defender Carrico has not featured since being hauled off after the first half of his debut against West Brom, which saw the Royals stage an amazing late comeback to win from 2-0 down.
McDermott said of the 24-year-old Portguese: "I spoke to Daniel on Friday. Putting him in against West Brom was a tall order, we've got to get him up to speed.
"He was Sporting Lisbon captain, you can see in training he's a good player and he just needs time. He needs time to train and to adjust. When he gets that, he'll be a good player for us."
McDermott also provided an update on the fitness of striker Jason Roberts, who has been out for almost two months.
He said: "He's got a hip injury, he tried to come back but broke down. He's trying to get back as quickly as he can and will be back as soon as possible."