The 22 year old defender returned to Shrewsbury in the summer of 2016 for his third loan spell with the club.
On loan from Fulham, Grimmer is capable of playing at right back or centre half.
Originally from Aberdeen, he started his career with his hometown club, before moving to Fulham in 2012.
He has gone onto play Championship football for the West London club and has represented Scotland at youth level.
In his first two spells at Town he helped them gain promotion to, and avoid relegation from, League One.
He also scored a 96th minute winner against Sheffield Wednesday in the 4th Round of the FA Cup in 2016, setting up a tie with Manchester United.