David Beckham has been recalled to the England squad for next Friday's friendly with Austria and the final Euro 2008 qualifying match against Croatia five days later.
"We've got to be so positive," McClaren said. "The disappointment is that it's out of our hands, that's the big regret.
"But we've got to hope that Israel can get a result against Russia. I thought all along the Croatia game at Wembley will be the decider and I still believe that."
Beckham is in line to win his 98th international cap in the friendly in Austria as McClaren finalises his preparations for the potentially decisive meeting with the Croatians.
"I checked on his injury, the injury is fine. He hasn't played many games but he's in the squad because with the likes of Rio and John Terry out we are lacking experience and big-game players - and David Beckham is one of them," McClaren said.
England squad: Robinson, Carson, James, P Neville, Campbell, Richards, Brown, Lescott, Shorey, Bridge, A Cole, Beckham, Wright-Phillips, Bentley, Gerrard, Lampard, Hargreaves, Barry, J Cole, Downing, Young, Smith, Crouch, Defoe, Owen.