England were placed in their perilous position after losing 2-1 to Russia last month in Moscow.
Former Premier League player Bilic believes England underestimated the other teams in their group.
"Because it is not easy to come to Croatia and to get something from a game," he added. "It is not easy to play in Russia. It is not easy to play Macedonia.
"And it's very difficult to play in Tel Aviv. So maybe you were expecting you were to cruise the group, but it's a very difficult group."
England manager McClaren is fighting to save his job, and the former Middlesbrough boss will come under enormous pressure should England not qualify.
But Bilic said: "As a club manager you need a couple of years to make or build a team.
"In a national team you need three or four years because you do not have them every day. You have them once a month for five days.
"It's not Steve McClaren's fault and I really feel for him and hope he is going to continue."
Watch the full interview with Slaven Bilic - Saturday, 1210 GMT, BBC One and BBC Sport website (UK only)