Chelsea paid big money to sign up German duo Kai Havertz and Timo Werner from the Bundesliga, and they both cost over £100m.
Timo Werner joined from RB Leipzig for a £47m, while Havertz cost £71m from Bayer Leverkusen.
Werner and Havertz struggled at first to perform, and Lampard has revealed that the intensity of the league was just too much for them.
“Timo was a big [signing] because Liverpool wanted him, Man United were in for him,” Lampard said on Sky Sports, The Overlap.
“We knew there were three or four big clubs [trying to sign him] so when I spoke to Timo I knew I had to be on my game to try and get him to come.
“With Timo and Kai, there was clearly going to be adaptation issues. I know that from being in it because they were shocked at the speed of training, they were shocked by the physical demands of the game.
“I remember Eden Hazard’s first year at Chelsea, he went on to be one of Chelsea’s best-ever players, but you looked at him in pre-season strolling around.
“Pretty much any player goes through those periods. Timo and Kai had that in the early days, Kai had terrible Covid as well which set him back quite a lot.”