Now that Chelsea are struggling for goals, have been scared by Crystal Palace and beaten by Sunderland in the space of a week and seen the season's first silverware opportunity go by the board, it seems obvious José Mourinho made a major miscalculation on the last day of summer transfer trading by assuming Samuel Eto'o would have more of an impact up front than Romelu Lukaku.

The latter's form at Everton is already embarrassing Chelsea, but under the terms of the deal he cannot be recalled until the end of the season.

Everton have him until summer, and they are using him to push towards the Champions League places. The doomsday scenario for Mourinho must be that Everton manage to grab a top-four spot at Chelsea's expense, returning Lukaku just in time for a run in the Europa League.

It is an entertaining possibility, but for several reasons it is unlikely to happen. Though strongest of the chasing group so far this season, Everton have won only half their 16 matches. The four clubs above them have all managed 10 wins or more, and whether Chelsea's form is stuttering or not, that makes the present top-four favourites to finish as the final top four.

For Everton to achieve a Champions League finish, three fairly unlikely things have to happen. One, they must continue playing well for the rest of the season, beating rivals such as Liverpool (at Anfield), City (Everton lost at the Etihad) and Chelsea (without Lukaku) when the head-to-heads come along. Two, one of the present top four (Arsenal, Liverpool, Chelsea and City) will have to drop out of contention. Three, Manchester United will have to remain out of the picture in mid-table and not complicate proceedings by climbing back into the reckoning in the second half of the season.

The last condition may not appear wholly unlikely at the moment, though United's next three games are against West Ham, Hull and Norwich, so it might be wise to check the situation again at the end of the year. The way Liverpool, and Luis Suárez in particular, have been performing suggests they are capable of remaining in the title race, not just the top four, for the foreseeable future. With City finally beginning to look ominously good, you could be looking at Arsenal and Chelsea as potential weak links in the present top four. Outrageous, I know, but even Mourinho would admit Chelsea are underachieving at present and there were signs at the Etihad on Saturday that all might not be completely happy within the Arsenal camp if important results remain elusive.

Those are the straws Everton must clutch at if they harbour hopes of a Champions League berth, and they are having a terrific season. Tottenham, who are not, have just sacked their manager on the pretext that they had no confidence André Villas-Boas could guide them to a top-four finish, and while the league table and the majority of Spurs fans would not disagree with that conclusion, the writing was on the wall as soon as Arsenal and Liverpool made such impressive starts to the season. Spurs must have been hoping to leapfrog their north London neighbours to claim a top-four place, because at the start of the season, with no realistic prospect of Chelsea, City or United dropping out, Arsenal appeared the weakest link.

No sooner did that perception change and United fall off the pace than Liverpool stepped up to take advantage. So even if United fail to rally this season, there are still two north-west clubs and two London clubs ahead of Everton and Spurs. If Spurs were hoping to make a significant gain on Liverpool at the weekend they were sadly mistaken. They could not make a top-four spot last season with Gareth Bale in the side, and the best that can be said of his replacements is that between them they have so far failed to come up with the galvanising effect the Welshman managed by himself in the past. If you were invited to put money now on Spurs finishing above United in the table, never mind cracking the Champions League or getting past Arsenal, you probably wouldn't be trampled in the rush.

The only thing that could dramatically upset these calculations is a staggering piece of business in the January transfer window that drastically alters the dynamic between leading clubs, though we know from experience that that is a rarity. You occasionally get staggering pieces of business, such as the Andy Carroll-Fernando Torres last-day drama of January 2011, though that season only Newcastle emerged from the transaction demonstrably better off, even if Torres did go on to Champions League success a year later.

Yet Chelsea find themselves in need of a striker, Liverpool have a very useful one, and the mischief-maker in Mourinho might fancy testing Anfield's determination to keep hold of Suárez with an astronomical bid. So might Real Madrid, for that matter. It is generally assumed that Suárez could move on at the end of the season, and that a substantial bid from a dream destination in Spain might not be resisted even if Liverpool are back in the Champions League by then, though there is no guarantee that matters will be resolved that neatly.

Liverpool are sensibly trying to tie Suárez to a new contract to protect themselves against predatory interest in the summer, though in point of fact he is a highly desirable commodity right now. Not only is he in the form of his life, scoring goals for fun, picking up awards and putting past controversies behind him, he is fully free to play Champions League football in the second half of the season. That, as any manager looking to make a killing in January will tell you, is a rarity.

When Chelsea paid £50m for Torres nearly three years ago, he was far from in the form of his life, and neither did his performances pick up on joining a new club. Goodness knows what price Suárez in his present mood would fetch using that as a guide, though there seems no good reason why Liverpool should expect offers to start arriving only at the end of the season. Most top players are cup-tied in some way by this stage. This one isn't.

If Suárez does stay at Anfield past January, there is no doubt Liverpool can be regarded as serious Champions League contenders. This is a new development since last season, and it means someone new will have to miss out. At the moment that looks like Manchester United, and Brendan Rodgers will be feted on Merseyside should that happen, but nothing is yet set in stone, least of all this season's top four.