Before moving to Motherwell in January 2015, Johnson had spent his career in non-league with spells at the likes of Solihull Moors, Kidderminster Harriers and Hednesford Town, but it appears that his time in Scotland and the Kassam Stadium has helped him emerge as a transfer target for a Premier League club.
According to The Sun, Leicester have shown a desire to take the 26-year-old to the King Power Stadium during the summer transfer window.
The approach appears to have materialised through Michael Appleton, the former Oxford boss who has become a part of Craig Shakespeare's backroom staff at the 2015-16 Premier League champions.
Last season, Johnson contributed three goals from 39 appearances in League One as Oxford narrowly missed out on a place in the playoffs.
It has been suggested that they value Johnson - who is also a target for Aston Villa and Birmingham City - at £2m due to previous club Motherwell being due a percentage of any transfer fee.