The England-born Scottish Under-21 international, who has played 14 matches so far for the Steelmen this season, has marked his presence in the Scottish Premiership with two goals and three assists.
Johnston can play both in defence and midfield, and he has regularly featured for the Steelmen since January, keeping his slate clean without a single booking.
He is out of contract at Fir Park in the summer, and his versatility on the pitch is attracting interest from across Europe.
Burnley, who have secured promotion to the Premier League for next season, are keen to sign him in the summer but now are expected to face a challenge from Luton when the transfer window opens in July.
The prospect of playing in the Premier League may be an attractive one for Johnston.
The defender spent the first half of this term on loan in the Scottish Championship at Cove Rangers.
Johnston has featured for Motherwell against both Celtic and Rangers in the Scottish Premiership.
