The Eredivisie side - who have won the competition in its previous UEFA Cup format - struggled against the Bulgarian champions and slipped to a 2-0 loss, leaving Cocu far from impressed.
Having missed out on a place in the UEFA Champions League following a qualifying play-off defeat against Milan, PSV were expected to top Group B, which also contains Chornomorets and Dinamo Zagreb.
However, defeat to Ludogorets extended PSV's winless run to six games in league and cup comptition.
"We lacked sharpness," admitted Cocu. "I told the players they should never underestimate the strength of the Bulgarian champions, they have a fine style of play and defend aggressively.
"They threaten on the counter, whereas we were hardly able to create any meaningful chances, which is very disappointing."
PSV face rivals Ajax at the Philips Stadion this weekend, with Cocu confident of a reaction from his players.
"We are looking forward to Sunday's clash at home to Ajax," he said. "It’s a big game and hopefully we will be driven by a desire to make amends for (Thursday's) defeat and performance."
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