Pompey are six points from Plymouth Argyle, who are third in the League Two table, after a disappointing 3-0 home defeat to Newport County on Saturday.
The former Chesterfield boss was speaking to BBC Radio Solent: "We have had too many inconsistencies this season, in my opinion, to be promoted automatically.
"The bigger teams that end up promoted have less inconsistencies. We have not put the team's above us under pressure."
He added: "It summed our season up in one game. We promised so much but failed to deliver."
Sixth-placed Portsmouth will be hoping to get back to winning ways when they travel to 11th-placed Mansfield Town in their next fourth tier clash this coming weekend.
Need a VPN? Or seeking to switch? Then support Tribal Football by clicking here to sign up with our official partners NordVPN. Not only will you receive the best VPN experience, but also great discounts by signing up via Tribal Football. Thanks for your support!