Lehmann's comments came as both sides get ready to face each other in a single Twenty20 on Sunday followed by three one-dayers and two Tests in the United Arab Emirates, reports the Dawn.
For Pakistan, it will be the first series in five years without Ajmal in the squad.
The talismanic off-spinner was suspended for chucking last month as part of a crackdown by the International Cricket Council (ICC).
In addition to being ranked the world's best bowler in one-day cricket, Ajmal is also the highest wicket-taker in T20s, with 85 scalps.
Lehmann, however, said Pakistan still has some very good players with exciting talent, and can never be underestimated.
Pakistan's T20 squad includes uncapped leg spinner Saad Nasim, while slow left-armer Raza Hasan returns after an almost two-year absence.
The UAE has been Pakistan's de facto home since 2009 when a terror attack targeting the Sri Lankan team bus in Pakistan resulted in the loss of international cricket.
It has proven a relatively happy hunting ground, with Pakistan famously registering a 3-0 Test victory over England in 2012.