Allardyce said, "Finishing fourth is looking increasingly tough."
"We should have finished fourth last season because everyone else was struggling.
"Now because of Liverpool's re-emergence, it makes finishing in the top-four much harder.
"Liverpool lost 14 Premier League games last season - they're not going to do that again in the next few years."
Meanwhile, transfer target and Trinidad & Tobago international midfielder Silvio Spann has confirmed he's received some interest from Premiership clubs.
Spann is a free agent and will be watched by Birmingham and Bolton scouts when T&T face Iceland at Loftus Road.
He told the News of the World: "There is some interest but for me, the main focus is playing for my country and ensuring I can make the World Cup.
"The coach has told me to make sure I take care of myself and pretty soon I will be playing with a club again."