Lincolnshire Police say they were called to the incident at the cash point outside Tesco on Wragby Road, at 4.29pm yesterday.
A 20-year-old man was arrested at the scene and remains in custody, while A 50-year-old man who was also arrested has been released with no further action.
The 17-year-old’s condition remains stable.
Any witnesses to the incident are advised to call 101 and quote incident number 299 for February 4.