Allen suffered a back injury and Milne picked up an ankle problem during training ahead of the team's departure for the five-match T20I series.
Allen, the powerful opening batter who has a T20I strike-rate of 163.60, would be certain of his place in New Zealand's T20 World Cup squad.
They have been strong performers for us in the T20 format since the last World Cup," New Zealand coach Gary Stead said.
The 21-year-old Foulkes took 14 wickets at 16.28 for Canterbury in the 2023-24 Super Smash and had a batting strike-rate of 150.
"Zak has had an impressive season for Canterbury including being their leading wicket taker in all three competitions," Stead said.
Tom Blundell has also been drafted in for the five-match series for which New Zealand were already missing a dozen players
Finn Allen and Adam Milne have been ruled out of New Zealand's tour of Pakistan raising concerns as to whether they will be fit for the T20 World Cup.
Allen suffered a back injury and Milne picked up an ankle problem during training ahead of the team's departure for the five-match T20I series.
Allen, the powerful opening batter who has a T20I strike-rate of 163.60, would be certain of his place in New Zealand's T20 World Cup squad. Milne, who has had an injury-hit career, is less assured of a spot in the final 15 for the USA and Caribbean depending on how many quick bowlers are taken.
"We feel for both Finn and Adam, suffering injuries so close to the start of the tour. They have been strong performers for us in the T20 format since the last World Cup," New Zealand coach Gary Stead said.
"Our support staff and medical networks will be working closely with both players over the next few weeks to complete plans for their treatment and subsequent return to cricket."
The 21-year-old Foulkes took 14 wickets at 16.28 for Canterbury in the 2023-24 Super Smash and had a batting strike-rate of 150. Blundell, New Zealand's Test wicketkeeper, has previously played seven T20Is.
"Zak has had an impressive season for Canterbury including being their leading wicket taker in all three competitions," Stead said. "He has displayed impressive skills with the ball, particularly in T20 cricket for the Kings. We also know he has skills with the bat and it will be an excellent opportunity for him to be part of the group."
New Zealand were already without nine players for the Pakistan tour due to IPL commitments while Will Young (county cricket), Tom Latham (paternity) and Tim Southee (strength and conditioning) were also not available.
Allrounder Michael Bracewell will captain the side with the squad also including uncapped batter Tim Robinson.
