Celtic signed Michael Duffy from Derry City during the January transfer window.
Duffy was brought to Parkhead from Derry City in the January transfer window, but he is still waiting to make his senior debut.
The 20-year-old has spent most his time playing for the development side so far and Frail admits there are still things that he needs to work on.
The academy boss saw Duffy come on in Celtic's under-21 side's match against Falkirk on Tuesday and feels that he is too wasteful in the final third at this moment in time.
“Michael looked bright and was more effective," Frail said. "He got at the full-back and his movement was good and he linked the play for us but he’s got to be more ruthless in front of goal.
“He had two or three really good chances, especially with the one that fell to him at the end where he wrapped his foot round it to place. He was maybe a wee bit too deliberate and the keeper made the save."
It is understandable that Duffy has improvements to make as he has made a big step up to join Celtic, but there are still high hopes for his future.
The skilful winger had looked very impressive whilst playing for Derry and he will be hoping that, in time, he progresses enough to play a key role for the Bhoys.
Ronny Deila has already shown that he is not afraid to play youngsters in his senior squad, and Duffy will be hoping that he can play a part for his new side in the 2015/16 campaign.