After starring for the club's Under-23 squad at Premier League 2 level last season, 19-year-old Johnson has spent the summer with the first-team and featured in every pre-season friendly.
He has been with Leicester since joining the academy at the age of 10 and helped England to victory in the Under-19 European Championship last summer.
A defensive shortage could yet see Johnson, typically a right-back, included in the matchday squad when Leicester travel north to Old Trafford on Friday to kick off the 2018/19 Premier League season against Manchester United.
Harry Maguire is unlikely to feature after only just returning to training following his delayed summer break, while £3m summer signing Jonny Evans is also a potential doubt.
Rumour has it that Croatian centre-back Filip Benkovic is set to join Leicester from Dinamo Zagreb before Thursday's transfer deadline, while there are also gossip that the Foxes will additionally snag Freiburg's Caglar Soyuncu, recently an Arsenal target.
According to The Times, Leicester still expect a late bid from Manchester United for Maguire and could let him go for £65m. If Benkovic and Soyuncu are on board, the Foxes should be covered.