The 19-year-old joined the Spireites on a season loan but the forward has struggled with injuries and only started two games.
"I think it was just a case of things have not really worked out with the injuries he has picked up," Sheridan said.
"He has not really figured too much and I do not think he has caught up after his injuries getting his fitness back.
"They (injuries) have just been occurring too many times and too frequently.
"Norwich have been very good about it.
"He (Spyrou) totally understands.
"It is hard when you are a loan player and he is young as well and he is living away from home when you are not playing regular it can be difficult.
"He is staying in a house sometimes on his own, staying in a hotel sometimes on his own, he is only 19. He lives down south and it was just difficult.
"It is a totally different ball game if he was playing regularly.
"It is just a decision we have both made.
"I spoke to Neil Adams at Norwich who I know really well and we just thought for both parties the best thing to do was for Anthony to return to Norwich.
"We sorted it out last week and we move on from it."
Sheridan added: "I brought him in because I really liked him as a player.
"When he is on his game he is sharp and he scores goals but I think we just have not seen the best of him.
"Unfortunately for him when he was looking sharp in pre-season he gets this unfortunate injury - a thigh injury - which was a setback for him.
"It has been niggling and there have been one or two other little things which keep popping up.
"It is hard because Norwich wanted him to come here, I wanted him to come here to play games, but unfortunately he has not played enough football so hopefully he goes back there and gets back to full fitness and sharpness because he is a very good player which is why I brought him here.
"Unfortunately myself and the supporters have not seen what he can actually do which is a shame."
Despite Spyrou's departure Chesterfield still have options in the striking department with Tom Denton, Scott Boden and Mike Fondop.
Liam Mandeville, who signed for Town from Doncaster Rovers in the summer, has featured as an attacking midfielder for the Spireites but can also play as a striker.
"When I have got people fit I am leaving people off the bench so at this moment in time I am going to look at (Liam) Mandeville and give him a chance up there," Sheridan explained.
"I think I will be looking at Liam more than bringing another one in."