And while a weakened side exited from the FA Cup last week, Whelan believes promotion remains firmly on track.
He said: "Every team has a wobble at some time or another, and ours came over Christmas when we lost three matches in a row.
"I was away in Barbados when we played at Sheffield United but before the game I got a feeling we'd beat them and go on a five or six match unbeaten run in the league.
"We did win at United and I seriously believe we will push on and go up as champions.
"I think we are the best team in the league having seen all the others bar two play.
"The lads here would fight to the death for each other, they're a good footballing team, and Paul Jewell has instilled a confidence that they can beat anyone."
With his sights firmly set on promotion, Whelan is in no mood to break up the current squad by allowing players to leave the JJB Stadium.
Matt Jackson, Lee McCulloch and Ian Breckin have all now signed new contracts, negotiations over a two-year deal for John Filan are under way, while a "not for sale" sign has been slapped on Nathan Ellington, Leighton Baines and Jason Roberts.
Whelan said: "I'm sure there is interest in one or two of our players, but other clubs are wasting their time.
"The only player we would have to talk about is Nathan Ellington because of the clause in his contract – if someone offers £3m, we have to let him talk to them.
"But Nathan believes he will be playing in the Premiership anyway next season with us, and for all the lads, their wages would double overnight if they got promotion.
"Nathan is aware of that, he enjoys playing for Wigan and is still learning his game here.
"The clause was put into the contract by his agent when he signed, and sometimes you disregard things like that at the time – I'd never let such a clause go into a contract now.
"Remember we signed Nathan from Bristol Rovers three years ago, and if anyone had wanted to pay £3m then, we would have taken it.
"Since then, he has developed as a footballer so well and we want to keep him here.
"We have been talking to him about a new contract, but I think he wants to see first if we get into the Premiership.
"If I was him, I would wait and see whether we go up and then start talking."
Ellington is one of a number of first team regulars who will return at Millmoor after being rested for the Derby cup tie.
McCulloch, Baines, Nicky Eaden and Jimmy Bullard are the others, but there won't be a debut of any sorts for new signing Andreas Johansson.
The Sweden midfielder will travel to South Yorkshire, but his lack of match fitness will leave him watching the game from the stand.
Johansson may soon be joined by another new signing at Latics as Jewell revealed he has made an approach for a transfer target.
He said: "I'm waiting for his manager to get back to me, and that would be a permanent signing if we can swing it."