Having made a promising start to his campaign when third at Down Royal, last season's Cheltenham Gold Cup hero was well fancied for Kempton's Christmas showpiece.
But after matching strides with defending champion Frodon for much of the way, Minella Indo soon weakened out of contention and was eventually pulled up by Rachael Blackmore.
Speaking at Leopardstown on Wednesday, De Bromhead said: "He was shook when he came off the lorry.
"When he came back from Cheltenham, he was as burly as he always would be, (but) I've never seen him as tucked up and tightened up as he was the other day.
"I might have been trying to put a square peg into a round hole, I don't know.
"The most important thing is to get him back now and get him as good as he can be for the spring, which is when he always seems to turn up in fairness to him."
Bookmakers eased him to a general 10-1 chance to defend his Cheltenham crown in March.
A Plus Tard chased home stablemate Minella Indo in the Gold Cup - and having made a spectacular comeback in the Betfair Chase at Haydock last month, the Cheveley Park Stud-owned gelding was a warm order to make it back-to-back wins in Leopardstown's Savills Chase on Tuesday.
After eventually mastering long-time leader Kemboy, the seven-year-old was denied in the last stride by Galvin, but De Bromhead is taking the positives out of defeat.
"There's not a bother on him - absolutely great. He ran a cracker and I was delighted with him," the trainer added.
"The winner was very good and obviously Kemboy's record around here is second to none. I was amazed he was short (in the betting) as he was, our fella.
"But he ran a cracker and jumped great - they're the positives. We just didn't win, sadly."
Envoi Allen got back on the winning trail for De Bromhead and Cheveley Park with a workmanlike display in Monday's Paddy's Rewards Club Chase.
While some were not all that impressed by the way he dispatched of the only other finisher Battleoverdoyen, De Bromhead said: "I thought he was really good - I was delighted with him.
"He jumped brilliant - he jumped so well at pace, I think.
"He beat a 155-rated horse and ran to his mark as far as I was concerned. He toughed it out and any time you win a Grade One is a good day.
"We'll enter him for the Champion Chase and the Ryanair at Cheltenham and see nearer the time."
The Waterford-based trainer also provided an update on last season's Grand National hero Minella Times, who fell on his reappearance in the John Durkan at Punchestown.
He added: "Minella Times is good. I'd imagine we'll enter him in the Thyestes Chase (at Gowran Park) and there is a two-mile-five-furlong handicap here (Leopardstown). He was second in that last year.
"We'll look to run him in and around there and aim towards the National."