Pedro Caixinha has recruited eight players so far in the transfer window - seven from overseas.
Ferguson, who had two spells at Rangers, says new players may be taken aback by the Scottish environment and the level of expectation on them.
"These guys will need to get up to pace pretty quick," Ferguson told BBC Radio Scotland's Sportsound.
"There's no doubt in my mind that they're good players.
"It's a bit easier to a certain extent at Ibrox where there's a bigger pitch and you've got 50,000 fans behind you but when you go to the smaller grounds, where it's tighter, the pitches aren't as good, they get the fright of their life.
"It's 100-mile-an-hour stuff. If you're not up for the fight, when you got to places like Easter Road or Tynecastle or Fir Park, these guys are going to run over the top of you.
"They're used to a different type of football. Scotland is a tough, tough, tough place to play football."
Portuguese defenders Bruno Alves and Fabio Cardoso and compatriots Dalcio and Daniel Candeias, who play in wide attacking roles, as well as Colombian striker Alfredo Morelos and Mexican duo Carlos Pena and Eduardo Herrera - a midfielder and a striker - have joined Scottish midfielder Ryan Jack in moving to Ibrox this summer.
"I don't know too much about most of the signings," said Ferguson. "Obviously, I know Bruno Alves, who has got 90-odd caps for Portugal. I've seen him play quite a bit. He's an experienced centre-half and a really good player. And Ryan Jack, I know obviously [from his time at Aberdeen].
"I've got to take my hat off to Pedro Caixinha. He's come in and he's identified that he's needed quite a lot of players. He's done his homework early and he's made a lot of signings pretty early as well.
"My only worry is, there's quite a lot of foreign players. In my time when foreign players came in to Rangers, they got the shock of their lives with demands that are put on them, the pace of Scottish football.
"It'll be interesting to see how they settle in. I still believe that you've got to get a spine at least of Scottish players. I know he's after Graham Dorrans, who I think's a fantastic player - and obviously, I saw yesterday, Kenny McLean as well.
"You can't lose your identity. You've got to have Scottish players.
"Many a player's come in who had 30-, 40-odd caps, who had played in big leagues over in the continent and they couldn't believe the pressure that they were under. When you play at Rangers, you're expected to win every single game.
"I believe that you've got to give him two or three months and you've got to give these players two or three months to settle in but again you don't get much time when you play at a club like Rangers."
Former Rangers captain Barry Ferguson believes the club's new signings will need to adapt pretty quickly.