Beagrie made the comments in the build-up to the Championship game between Forest and Middlesbrough at the City Ground on Saturday afternoon.
While praising the work done by the Reds in the summer transfer window, the 49-year-old said on Sky Sports 1: “Some of these players that we didn't really know have been exceptional, the left-back Pinillos being one of them. He has been absolutely tremendous.”
Pinillos joined Forest on a two-year contract in the summer transfer window after leaving Spanish club Cordoba at the end of the 2014-15 season.
The 22-year-old left-back has proved to be a good signing and has played well for the Reds so far this season.
In five Championship appearances this campaign, the youngster has created one chance, has a pass accuracy of 73%, and has won five headers, five dribbles and eight tackles.
Forest are 12th in the Championship table at the moment with 11 points from eight matches, just a point behind sixth-place Reading.