"He was a great guy and one that plenty of people will miss, but never forget."
Others took to social media, describing Muir as the nicest person "they had ever met" and an "amazing character".
Muir worked for the Ashburton District Council as an apprentice gardener.
A council staff member said it was too soon to comment but the council would make a statement later in the week.
It is understood that the driver of the car raised the alarm after summoning help from a nearby house.
The 22-year-old was taken to Ashburton Hospital in a serious condition but released over the weekend.
Until the Serious Crash Unit has completed its investigation it is whether charges will be laid.
- Ashburton Guardian