Dristvaathu Paandavaaneekam Vyoodham Duryodhanastadaa
Achaaryam Upasamgamya Raajaa Vachanamabraveet ||
But then, he knows that, Pandavas are themselves very Great warriors. Arjuna among them is almost undefeatable by either humans or Gods or demons. Duryodhana's greatest worry in the war is about Arjuna.
Arjuna had defeated the Kauravas headed by Duryodhana already once, in a battle called Uttara Gograhanam. Arjuna had also saved them once from a Gandharva King, when the Gandharvqa King defeated them and enslaved them. Now, Arjuna is even more powerful - having acquired several celestial arms from Indra, the king of Gods and the most invincible weapon of all, called the Paasupataastra, from Siva himself.
Vyoodham Drupada Putrena tava sishyena Dheematha ||
"O Master, Look at this Great Army of the Pandavas, arrayed against us in a particular way, by your talented student, Dristadyumna, the son of Drupada."