The talented youngster had been a long-term target of Cobblers boss Colin Calderwood, and despite attracting further interest from other League clubs, finally settled on a move last week.
The club will receive a five-figure sum for the young defender as well as benfitting from appearance bonuses and a sell-on clause.
Boss Terry Brown is naturally disappointed that the young centre half chose to leave, but believes Johnson will step up to the challenge.
He told the paper, “We wish him all the best, Brett really deserved this as out of all the young lads he really developed the most last season and grew into a proper defender. I'm sure he will break into Northampton's first team and go on to have a successful League career,” said Brown.
But aside from the disappointment, Brown said he did hope to have one new signing on board by the end of the week, with the player likely to be a striker.
“We're in talks with players this week and ideally I'd like to have a forward signed on by the end of the week. I think we're really looking for about five players, but it doesn't really perturb me that we haven't got them in yet and it won't until we're well into the pre-season,” said Brown.
Currently the boss has just enough players to make up the back line, with the chance for injury-hit defender Tobi able to break into the first team.
“Tobi had a disappointing season last year largely due to injury, he did break into the first team and this will be his chance to step up. I had a couple of the boys in last week to check on their fitness and Tobi is looking very fit which is good news.
“We've got John Brough in there, but I'm still looking for another defender, there's two schools of thought, get someone experienced in or get a youngster in, someone like Will Antwi,” said Brown.
However the boss is well aware that for the first two games of the season, he will be without Darren Barnard, who serves out a suspension from the Play-Off semi-final game at Carlisle.
With thanks to the Aldershot News.