Tidal Bay is a doubtful runner in Saturday's Argento Chase at Cheltenham.
The 12-year-old won the Grade One Lexus Chase at Leopardstown over Christmas but Paul Nicholls says he is "odds against" to run at the weekend.
The champion trainer told Betfair: "After working this morning, he came back slightly lame. Myself and Clifford (Baker, head lad) have looked him over and the problem is hard to diagnose. It could be either an infection brewing in his off-hind foot, and or he has pulled a small muscle, but we don't know at the moment."
Nicholls added: "We will obviously monitor him in the next 24 hours, and then make a decision on his participation.
"It isn't a serious problem - and he may well yet run on Saturday - but I thought it was best to keep everyone informed. At this stage, though, I think it is odds-against him running at Cheltenham at the weekend."
The Argento has already lost its headline act, with Gold Cup favourite Bobs Worth ruled out by Nicky Henderson.
Nicholls has also raised the possibility JCB Triumph Hurdle favourite Far West may not have another run before the Festival. The four-year-old is unbeaten since arriving from France, winning at Chepstow and twice at Cheltenham.
Nicholls had suggested Far West could run this weekend in the Triumph Hurdle Trial, but he will instead saddle either Sametegal or Irish Saint in that contest.
"I was always going to run one of the other two this weekend. There's no plan with Far West, he's completely A1, though. I haven't been searching for another race for him and it wouldn't be crucial that he even had another run before the Triumph," said the Ditcheat handler.
29 July 2015Tributes pour in for O'Sullevan
It's Shanahan's turn at Galway
Sir Peter O'Sullevan dies, aged 97
Kachy not for catching in Molecomb
No Sussex regrets for O'Brien
Solow flying high at Goodwood
Highland reels in Gordon rivals
Fortune favours Twiston-Davies
Peacock pair vie for Galway glory
Shalaa in top trim for Richmond
Dunlop excited by Trip to Goodwood
Moviesta gets King George go-ahead
Karakontie has Deauville date
Dog delivers for Mullins and Walsh
Tint proves Topaz jewel
Maguire back in the saddle
Blue back with a bang
Tough Toormore takes Lennox glory
All roads lead to Arc for Postponed
Logan shines for Kirby
Frankie grabs Gold at Goodwood
So seeking Sussex success
28 July 2015King targeting Molecomb reign
Mullins hoping Bob is back
Wayman lands BHA role
Medrano eyeing Gordon glory
Options open for Force
Group race aim for Nisser
Modem takes control
Solitaire shines in Weld double
Bach in business
Vastonea out to sparkle in Topaz
Tanzeel unlikely for Cup date
Birch bids for Vintage victory
Toor targets Lennox triumph
Gleneagles misses Solow clash
Charlton eager for Golden Test
27 July 2015Modem takes control
Bach in business
Morny 'ideal race' for Gutaifan
Fahey ponders options for Guest
Perth double-header a washout
Sovereign option for Kodi
Salisbury option for Salvo
Group One trio top Nassau entries
Rain claims Tuesday Perth card
Perth card in doubt
McDonald nets Carlisle hat-trick
Mondialiste impresses in Pomfret
Injury in stalls forces Pilot out
Coleman lands Ferguson role
Gutaifan takes Papin honours
O'Brien plots Goodwood Air raid
Toormore seeks Lennox redemption
Buratino to take flight in Phoenix
Sovereign too soon for Elm Park
26 July 2015Lonsdale aim for admirable Cookie
Murphy looking for Top performance
Rizeena to chart Rothschild route
Erupt firing for Niel Arc prep
Meade sweet on Hugh's for Kurland
Newland considers Pineau future
Injured McCullagh 'very stable'
Ship ready to Fire in Pomfret
BHA to launch Bid inquiry
Post delivers in King George epic
Horn set York mission
Speedy Tanzeel downs Dash rivals
Guest is heaven sent for Fahey
Tullius topples Tonto at York
Goodwood heroes back for more
Besh the best in Princess Margaret
Sixth Sense an Ascot blockbuster