The four-times Grade One winner had been quietly fancied for the great race, but he is instead likely to be preserved for the Punchestown Festival.
Frank Berry, racing manager for owner JP McManus, said: “Carlingford Lough will not run.
He needs a bit more time and will probably go to Punchestown.”
Carlingford Lough, trained by John Kiely, was last seen finishing fourth in the Cheltenham Gold Cup and was available at around 22-1 about winning the National.
Berry confirmed that McManus would still have five contenders after Monday’s five-day declaration stage but that retained rider Barry Geraghty would not be rushing into a decision over his mount.
Gilgamboa, Gallant Oscar, Pendra, Shutthefrontdoor and Cause Of Causes are all still in the mix for the powerful owner.
Berry said: “We’ll confirm five, but I’ve had no indication yet from Barry as to which way he’s leaning.
“We’ll see how they are all nearer the time as a lot can happen with horses in a week.
At this stage, though, they are all in good form. He might be waiting to see if Cause Of Causesgets in but I wouldn’t be very hopeful of that.
Meanwhile ante-post favourite Village Vic is among 44 horses standing their ground at the confirmation stage for the Crabbie’s Topham Chase at Aintree on Friday.
The Philip Hobbs-trained nine-year-old enjoyed a fruitful winter, winning four races on the bounce, including the Caspian Caviar Gold Cup at Cheltenham in December.
However, his successful streak came to an end at the Festival after he was a well-beaten ninth to Vautour when stepped up in class for the Ryanair Gold Cup.
His main market rival in this appetiser over the Grand National fences is the Colm Murphy-trained Empire Of Dirt, who was victorious at Cheltenham in the Brown Advisory & Merriebelle Stable Plate Handicap Chase.