The 16-year-old was attacked at the fast food restaurant on Ravenswood Avenue in Ipswich at about 7.30pm on Wednesday.
It is the third stabbing in the town over the past two weeks.
He has suffered life-threatening injuries and was rushed to hospital.
Four people have been arrested in connection with the attack, Suffolk police said.
It comes after a man in his 20s was stabbed more than 10 times in his torso and legs on Monday.
The attack on the victim, whose condition has been described as serious but stable, was not being treated as linked to the fatal stabbing of Tavis Spencer-Aitkens, 17, on 2 June.
More police are being deployed in Suffolk following the attacks.
This is the early stages of a live investigation where we are already managing a significant number of enquiries, detective chief superintendent Simon Parkes said.
The public will see an increased number of officers in the area. I would urge anyone who has any information which may be relevant to call Suffolk Police.
Witnesses should call 101 quoting reference CAD 355 of 13 June or Crimestoppers anonymously on 0800 555 111.
News Source SkyNews