The former Cambridge and Southend man was particularly unhappy with his performance during Saturday's 1-0 derby defeat to MK Dons, and he has asked the club's supporters to be patient with him as he gets his game back together.
Guttridge endured a frustrating season with Colchester United in the Coca-Cola Championship last season, playing only a handful of games before being released in the summer.
He spent the close season trying to win a new deal at various clubs before signing for the Cobblers, and that meant he was unable to get through a proper pre-season, something he is paying for now.
Guttridge is now playing fitness catch-up while also playing first team games, and he admitted: "It's going to be tough, but I have set myself goals.
"You don't really get the chance to catch up because you are thrown in at the deep end.
"Against Cheltenham I played the 90 minutes, and then at Millwall at the start of the second half I did three or four sprints, I went to push, and there was nothing there.
"You know from then on you won't regain that.
"But if you have had a good pre-season, you know you just need a five-minute break, sit in a little bit, and you will be fine.
"So I am disappointed at the moment that I can't produce and play the way I would like to, but that will come in time."
And he added: "It is very hard for me at the moment because I am playing a restricted game.
"I know I am not fit enough, the manager knows I'm not fit enough, and I'm caught between a rock and a hard place.
"On Saturday I was very disappointed with the way I played.
"It looked like I was having too many touches, but it wasn't that I wanted to have those touches, it was that I simply couldn't get the ball out of my feet."
Saturday aside, Guttridge says he is revelling in life at Sixfields, and said: "I am having a great time here, and they are a great set of lads.
"I could have gone to other clubs and had chats with other clubs, but they just never felt right.
"The lads at Northampton were welcoming, I enjoy the training, and it's just nice to be playing football every week because last season was a washout for me."

Former Cobblers director of football John Deehan was at stadium:MK at the weekend, and will have been running the rule over his former club.
That's because Deehan is now employed as a scout by Premier
League outfit Bolton
Wanderers, who Town play in the Carling Cup second round at the Reebok Stadium next Tuesday night.