Barnes said: "The derby win should give Liverpool a lot of confidence because they are now only four points behind Everton and Everton have got the harder run in.
"Saying that, Liverpool haven't really put that many good performances and results together this season so it's difficult to say for certain what will happen next.
"It was a fantastic performance and result against Everton, it gave everyone a lot of hope. But the injuries that came out of that game, added to the ones they've already got, will make life difficult for them.
"It is going to be even more difficult for them now because of the injury situation. They are without a recognised striker now and that could have an impact.
"A lot will depend on how long it takes Morientes to get fit. They may have Luis Garcia back for the Bolton game but apart from that they don't have anyone else to play up front.
"Once upon a time you would have expected Liverpool to have closed the gap on Everton by now because of Everton's inconsistency over the last few weeks.
"But Liverpool have been so inconsistent too. So while the Bayer Leverkusen and Everton results and performances should give them heart the key thing is how they will cope with the loss of so many strikers.
"They don't have any available now, I don't see any. They could put Smicer and Garcia, if he's fit, in attack against teams who are either fighting for Europe or fighting for their lives.
"It is going to be very difficult over the next few weeks without any frontmen but I still feel Liverpool have enough quality to over-take Everton by the end of the season. How quickly, or how comfortably they can do it, depends on how long it takes Morientes to recover.
"I still expect Liverpool to finish fourth but I'm not as confident as I was. Morientes won't play against Bolton and probably Manchester City and there is no-one else to come in with Baros suspended so it is going to be tough.
"I think the fight for fourth place will go down to the wire. For three or four months we have all expected it to be between Everton and Liverpool but Bolton are not far behind now. It all depends on who finds the consistency. If neither Everton or Liverpool can find it then there is no reason why Bolton cannot snatch fourth place."