Parkinson admitted that he was disappointed with the defending on show from his players against Oldham on an afternoon when the Bantams fell to a 3-2 home defeat.
The Bantams chief said that he would also have to look into reasons for the club's curious recent home form after Lee Johnson's Latics became the third away side in four games to leave Valley Parade with all three points.
While the Bantams have taken seven points from their last four away matches and conceded only twice, they have also only picked up one point from the same amount of home matches while conceding nine times in the process.
With Oldham enjoying a free week in the build up to this Saturday's fixture while City played against Coventry City on Tuesday night, Parkinson pondered post-match as well as to whether three games in a week with largely the same starting eleven was perhaps a bit too much for his side.
Looking back at City's defeat to Oldham, Parkinson said: "We haven't defended today (Saturday) as well as we have done in previous games.
"I know that might sound an obvious thing to say, but we really did give some poor goals away today.
"If you look at us at Leyton Orient and Coventry, I think we put in two of our best defensive displays of the season. We were superb and picked up two clean sheets. We needed to produce that again today - the same solid approach as before would have sufficed - but we have to be honest and say that we didn't deal with the big moments in the game.
"At one-one, we are right back in the game but we concede right on the stroke of half time.
"That was a key moment in the game.
"After being behind, to get in level at half time would have been a big lift for us.
"In the second half, their third goal was another poor one for us to concede and it gave ourselves a mountain to climb.
"We did look like a team who lacked energy.
"I've picked roughly the same side three times in seven days and I need to look at myself for that.
"Equally though, when you concede goals in the way we did today, it really gives the opposition a lift. You could visibly see how Oldham rose after their goals and how they were sharper all over the pitch.
"I felt that their extra man in midfield was difficult to contend with today. It's a system - 4-5-1 - that is a great one if you get the lead away from home because you can play on the counter-attack.
"They were very difficult to break down and we didn't have enough creativity in the team to look like we could break them down.
"We have to look at ourselves because the last couple of home games we have been disappointing.
"In the last couple of years, and even this year when we've been struggling for wins and only getting draws, the performances were a lot better at home than the last couple.
"We have to look for reasons for that and try to resolve things next time we're at home."
After mentioning plenty of times in the build up to this weekend's game about City still having work to do to secure safety despite going into the Oldham game nine points clear of the bottom four, Parkinson knows a big effort is now needed from his side in the club's remaining five games of the season after their gap to the drop zone was cut by three this Saturday.
Parkinson added: "When we got to 49 points, I think a lot of people felt that was safety because we were nine points clear (of the bottom four), but teams are going to get wins you don't expect, like we did at Leyton Orient.
"People didn't expect us to go there and win but we did. Other teams will pick up points as well though.
"A lot of the mid-table teams have lost (today) and a lot of the sides near the bottom have won so it has tightened up the division again.
"It is still completely in our hands though. We are six points clear with a better goal difference, but we need to play better than we did today.
"We certainly have done over the last seven days - we've been superb - but we need to regroup now and make sure in the next game we are a lot more solid in our defending than we were today."