Martin O'Neill's side may be in an elevated position in the Premiership, but a promising season is suddenly becoming more difficult by the day.
Any hopes of Uefa Cup glory, as the club tested the European waters for the first time in 36 years, were quickly banished by Spain's Atletico Madrid and the brilliance of Brazil's Juninho.
Further misery soon followed with the first Premiership defeat of the season at Filbert Street coming at the hands of local rivals Derby via a double from the Italian Francesco Baiano.
However, there were no Continental forces at work in last night's Coca- Cola Cup humiliation, just sheer typical English grit and determination from Alan Buckley's battling Grimsby - characteristics which carried Leicester to long overdue glory in April.
But the cup holders relinquished their grip on the trophy they won with such pride and passion, as they were first rattled and then humbled by the Mariners.
Three goals in nine minutes during the second half was Grimsby's just reward for their never-say-die attitude - a facet of Leicester's make- up which seems to have disappeared.
Keller, who produced a string of outstanding saves during that second period which saved Leicester from more embarrassment, said: "We are better than that - much better than that. But we need to get back to the Leicester that everybody knows, up the work-rate and try harder like we know we can. We have put ourselves in a good position so far, but there's a long way to go in the Premiership season just to ensure we stay up."
The United States international added: "We have no right to be in this League and no right to be in fourth place. You have to fight for everything you get just like every other team does. We are about being a hard-working team, an honest team that fights for one another until the end of a game. Now it's time to get back to it."
However, injuries are beginning to hamper Leicester's season as the captain, Steve Walsh, could be out for another month after cracking a rib, despite initial reports suggesting he had broken his arm.
Walsh, who only returned to the side last night after three weeks on the sidelines with a hamstring injury, will be joined in the treatment room by his fellow defender Julian Watts who suffered concussion and facial injuries.
Watts definitely misses this Saturday's game at Chelsea, and O'Neill is now in the middle of a crisis as he was also without five-first team regulars for last night's disaster.
Meanwhile, the Grimsby defender Kevin Jobling is hoping to land a new contract from the club as he has been on week-to-week terms since the start of the season. His first goal in Town colours for nearly three years could help him go a long way towards achieving his aim. He said: "I was in nosebleed territory when I scored."
The 28-year-old, who started his career with Leicester before moving to Blundell Park in 1987, added: "I don't score many but when I do they are important. But I'm just trying to earn myself a new contract and hopefully I can do that."Reuse content