10. Leighton Baines
After Patrice Evra's form started to slide last season, a new left-back was a top priority for Manchester United in the summer. The Reds baulked at Everton's £15million asking price for Baines, though, and instead chose to root in the Euro bargain bin, picking up Holland's "third or fourth" best left-back for only £4million. It's a move that hasn't really worked out, with Alexander Buttner struggling to impress thus far and Baines continuing to show his quality in another excellent season at Everton. Still, at least Evra is showing signs of improvement.
9. Mohamed Diame
According to reports, Liverpool had practically agreed a deal to sign Diame before Kenny Dalglish was sacked in the summer. The midfielder's qualities may not fit in with Brendan Rodgers' philosophy but, as a free transfer, Diame could certainly have added an extra bit of steel to the Reds' squad. The 25-year-old demonstrated the impact he can have from the bench when he came on at half-time to change the game in West Ham's 3-1 victory over Chelsea, and Liverpool could have benefited from having the option of an all-action midfielder in reserve. It's been reported that several clubs, including Arsenal, are considering meeting Diame's £3.5million release clause in January, and Liverpool may regret that they didn't push through their move in the summer.
8. Mathieu Debuchy
After qualifying for the Europa League last season, Newcastle needed to strengthen their relatively small squad to stand up to the challenge of fighting on four fronts. The Magpies were linked with a move for the impressive Debuchy all summer, but ultimately failed to add significant quality and numbers to their ranks. As a result, Alan Pardew's team have struggled with injuries and key players losing form, and the manager has had to rely on the club's youngsters to step in. With Newcastle languishing in 14th, it's unlikely a player of Debuchy's calibre would still be enticed by a move, and more additions really should have been sought in the summer.
7. Michael Dawson
QPR were linked with a £10million move for Dawson towards the end of the transfer window and, after conceding 29 goals so far this season, it's clear they could have done with a centre-back of his ability. Instead, the Rs have been forced to continue with old heads Ryan Nelsen and Clint Hill, while Anton Ferdinand has struggled for form and fitness this term. Harry Redknapp may be keen to resurrect a deal for Dawson in January, but the England defender is unlikely to join a club that already has one foot in the Championship.
6. Marouane Fellaini
Along with Mousa Dembele, Fellaini should have been high on Man United's list of summer targets given their long-standing problems in midfield. The Belgian has been hugely influential in Everton's solid start to the season and his ability to take matches by the scruff of the neck is something United have lacked since Roy Keane's departure. After shelling out £15million for Fellaini in 2008, Everton would want big money for their star man, but his qualities are worth the Glazers relaxing the purse strings.
Fernando Torres may have scored four goals in his last two matches, but that's still one fewer than Falcao managed in Atletico Madrid's 6-0 mauling of Deportivo La Coruna at the weekend. The contrasting form of Falcao and Torres this season has highlighted Roman Abramovich's mistake in persisting with his record signing, although the Chelsea owner doesn't strike us as someone who has too many regrets. Falcao put the Blues to the sword with a stunning hat-trick in the Super Cup on deadline day, but at that stage Abramovich had already decided to indulge Torres for a little longer. It seems the Spaniard may slowly be starting to repay the owner's faith, but that shouldn't put Chelsea off a big-money move for Falcao in January.
Both Man United and Liverpool were linked with a move for Michu in the summer and, in hindsight, it was a huge mistake that neither coughed up a paltry £2million to sign the Spaniard. The 26-year-old may only have been back-up to Robin van Persie at United, but he would surely have started at Liverpool and could have forged an effective partnership with Luis Suarez. Michael Laudrup has suggested that Swansea would want £30million to part with Michu now, and the forward's 12 Premier League goals could have seen the Reds standing much closer to fourth at this stage.
3. Daniele De Rossi
Man City could have benefited from a player of De Rossi's quality on Sunday when they were stretched by Man United's ruthless counter-attacking and, as I said in 16 Conclusions, the club's summer business left much to be desired. City may have had one eye on FFP coming into force but, after winning the title last season, a further statement of intent was required to kick on both domestically and in Europe. De Rossi was linked with a move to the Etihad throughout the summer, but eventually reaffirmed his commitment to Roma, forcing the Blues into a late move for Javi Garcia. How Roberto Mancini must wish he had persuaded the Italy international to sign for the champions.
2. Demba Ba
How Demba Ba remained at Newcastle in the summer is beyond the great minds at F365. After the Magpies narrowly missed out on reaching the Champions League qualifiers, it seemed certain that someone would take advantage of Ba's release clause to sign the 16-goal hitman. As Sarah Winterburn said here, the striker guarantees goals and for a bargain fee of around £7.5million, Liverpool really should have made a move for Ba instead of signing Fabio Borini for more than £10million. With Borini failing to impress before his injury and the Reds still in desperate need of attacking recruits, Ba should be a top target for Brendan Rodgers in January. Perhaps Arsenal should also be keeping track of developments.
1. Mousa Dembele
We're big fans of Dembele at F365 and the midfielder has proved to be worth every penny of his £15million release clause after joining Spurs in the summer. Spurs have won six and lost just one of the seven matches Dembele has started this season, and the Belgian should have been top of Sir Alex Ferguson's list of targets to fix Man United's problem area in midfield. Dembele was superb in a late audition for a move to United when Fulham were beaten 3-2 at Old Trafford in August but, strangely, Ferguson chose not to pursue a deal. The manager may have regretted his decision after Dembele returned to help Spurs to a 3-2 victory over United in September and the club's title tilt would seem far more convincing with him in the team.
Matt Stanger - ask him about his summer regrets on Twitter.