The Saints signed the 22-year-old forward from Lille for a fee believed to be around £16million, but unfortunately he will now be missing for all of September.
Puel said: "Boufal has a little injury for the moment.
"He worked very well, every day, but now it's important he make good work with a strong knee. When he comes back with us he can play at a good level.
"I don't know [when he will be fit]. I think one month or more to get back to a good level."