Gordon Marshall says the biggest stumbling block to Celtic winning Sunday's Scottish Communities League Cup final against Kilmarnock at Hampden will be themselves.
Neil Lennon's men are 21 points clear of administration-hit Rangers at the top of the SPL and kept themselves on course for the Treble with a 4-0 win over Dundee United in the William Hill Scottish Cup quarter- final at Tannadice.
Marshall has experience of playing in finals with both Kilmarnock and Celtic, having kept goal for the Hoops side which infamously lost on penalties to First Division Raith Rovers in the 1994 League Cup final at Ibrox.
In 2001, he was playing for Killie when Henrik Larsson scored a second-half hat-trick to land Martin O'Neill's first trophy in the Irishman's debut season.
Marshall – currently goalkeeping coach at Motherwell – claimed Celtic have to guard against complacency.
"Celtic have to be favourites, they are the best team in Scotland and playing well going into the final," he said.
"Obviously the league looks as if it is going to take care of itself so they have to go for the two cups to get the clean sweep. The only problem Celtic might have is Celtic. They have got to make sure they have the right attitude.
"When I was in the Killie team who played them here, Larsson was probably the only one who was scoring goals.
"Now they have Stokes, Hooper and Samaras and they have been scoring a lot more from all over the park so I think Celtic's biggest problem is going to be Celtic.
"But Lennon and his staff know what it's like to turn up for these big days and I'm sure they will be well prepared.
"Kilmarnock will need to start well and score first because if you let Celtic score they become a difficult team to get two goals against."
While a Killie victory would be a shock, it would not come into the same category of cup final upsets as Raith's finest hour.
But Marshall warned the Celtic players that defeat would still take some time to live down.
"I get a wee bit of stick about Raith now and again," he said.
"The big thing with Celtic is you have to win every game and it's that mentality of win, win, win.
"So yes, there will be a lot of stick if Celtic don't win it but that won't be in the players' minds.
"They have been very ruthless recently so they will go in with the right frame of mind."