McDermott moved quickly to boost his ranks when the window opened at the start of the month, landing Hope Akpan from Crawley and Daniel Carrico from Sporting Lisbon.
The Royals boss then further shored up his leaky defence with the capture of right-back Stephen Kelly, who signed a two-and-a-half year deal with the club on Monday.
Yet with his team still three points from safety, McDermott admits he is still searching for yet more players before the window shuts in two weeks' time.
McDermott has been heavily linked with Celta Vigo forward Iago Aspas, and the Royals boss admits there is still a possibility that he will enter the market again this month.
"We have signed three, but we are still in the process of looking," McDermott told a press conference.
"There are a lot of complications trying to sign a player as everyone knows, but if something comes our way, we have the finances and he wants to play here then we will do something. There is no doubt about that."