"It wasn't the performance we'd hoped for. It was disappointing in a number of areas, I won't lie," Croft said.
"But the will is there and the effort will be put in this week ahead of the next match."
Glamorgan face Worcestershire in Cardiff from Friday, 14 April.
The Welsh county were beaten by an innings and 22 runs as they slumped to a third consecutive heavy loss in matches against Northants.
"I'm trying to balance out (my assessment), but I am very disappointed," Croft told BBC Wales Sport.
"The preparation you put into the game, you don't envisage the result at the end of it.
"What I and the players will be looking to put right is to rebuild the confidence, and ensure there's full commitment to a better performance.
"We've got a week of preparation where we'll be doing all we can to ensure a much improved performance."
Glamorgan were without Will Bragg, Timm van der Gugten, Michael Hogan, Graham Wagg and Ruaidhri Smith through injury, while David Lloyd was unable to bowl because of a hamstring problem.
Number three batsman Bragg, Glamorgan's top run-scorer in the 2016 Championship, is scheduled to play a second team game at Northampton after back trouble, to see if he has a chance of facing Worcestershire.
"It's in his best interest, he hasn't played any cricket for a long period so just to get back into the middle and see if his back flares up," said captain Jacques Rudolph.
"He was one of our best batters last year."
Hogan (sore hip) is the most likely of the seam bowlers to have a chance of returning.
Worcestershire will be without England all-rounder Moeen Ali, who is rested from their opening game on ECB instructions and will return the following week against Northants.
"They've got a pretty decent batting line-up as it is, and (Joe) Leach has done well for them with the ball, they're going to be a competitive team to play against" added Rudolph.
"But after this loss, it's important to work on what we can and not focus too much on the opposition."
Glamorgan won by five wickets at Worcester in 2016, after being on the wrong end of a rain-ruined draw in Cardiff.
Glamorgan head coach Robert Croft says his team will not lack for effort as they attempt to recover from a two-day defeat at Northampton in their first Championship match of 2017.