Substitutes are always a key factor when assessing a manager's decision-making. They are also always hotly disputed in the aftermath of a result, particularly if that result was a defeat.
First up; Modou Barrow. The Gambian winger is introduced at the expense of Wayne Routledge with 29 minutes remaining. Next up? Guidolin sees Ki Sung-Yueng, Leroy Fer, Bafetimbi Gomis and sends his warm-up orders to... Kyle Naughton?
It's the manager's fourth game in charge and it's also the fourth time he opts to bring on the former Tottenham Hotspur man to change things and swing the match in his side's favour.
Does it work? No. Has it worked in any of the three previous games? No. A straight swap at full-back, believe it or not, does not help the Swans to all three points as their mini-run of four games unbeaten comes to an end. Fourth time lucky doesn't occur and the assessment of the manager's decision-making that evening comes back with low marks.
Frequent, but puzzling, substitute
It's become customary under Guidolin to see Naughton brought off the bench to influence the game. Against Everton last month, he was used almost to time waste as he entered proceedings on the cusp of stoppage time in a 2-1 win. His introduction against Crystal Palace the week before the Saints clash was similar, with it making no difference eight minutes from time in a 1-1 draw.
Against West Bromwich Albion he was given a reasonable run out - just like against the Saints - as, just before the hour, left-back Neil Taylor made way for the primarily right-sided man. However, with no key passes played and just 67 per cent pass accuracy accumulated, how was his introduction justified?
Both Jefferson Montero and Barrow were unused substitutes at the Hawthorns that day, which is something many picked up on after full time once the Swans had dropped points late on - Salomon Rondon equalising in stoppage time.
However, one man who didn't pick up on it was Guidolin, who opted for the same change on Saturday. Naughton's impact this time was better, with him creating a chance and completing 83 per cent of his passes, but it was not game changing.
Attackers at the ready
Swansea's attack is becoming very predictable, which is especially bad news when they are at the wrong end of the table. Goals are needed more than ever, but they are not coming because of a lack of creativity. The pace and directness of a player like Montero is what the Swans need late on to win a game, not the slightly adventurous but controlled offensive threat posed by a right-back.
The change might be more understandable if Guidolin was bringing on Naughton to play on the wing, as he does possess good attacking qualities. However, simply introducing him as part of a straight swap at right back severely limits the impact he can have on the game, as he is obviously going to spend less time in the other team's half and, thus, the final third.
How much impact can a player have in an attacking sense when they spend half of their time defending?
With an attack-minded player like Fer yet to make his debut and a creative midfielder like Ki unused as he returns from injury, the use of Naughton at the weekend is even more baffling. At West Brom, it was the same. The right-back was chosen ahead of Barrow, Gomis and Montero, all of whom are attackers. It seems almost incredible for Guidolin to view his seemingly second-choice right-back as a better impact sub than these players.
Barrow has been a real livewire off the bench all season, posing all sorts of problems, whilst Montero has done the same when given the chance. Gomis may be enduring a poor run of form, but the chances of him scoring and breaking his duck are certainly better than Naughton's.
Furthermore, Angel Rangel has been the player that Naughton has been replacing under Guidolin, bar one instance when it was Taylor. The Spaniard, however, offers just as much as his English teammate and fatigue never forces him off either.
If it is the wings where Guidolin believes Swansea need refreshing during games, why is he looking at Naughton over Barrow and Montero? Alternatively, if it's Naughton he believes can change the game, why is he limiting his effectiveness by deploying him at right-back, and not putting him ahead of Rangel out wide and trying something different?
There are so many angles at which the customary substitute can be criticised, and all lead to the same conclusion being drawn. That is, that the change is not working and that either the role Naughton is being brought into needs to change, or the player being introduced does. With so many attacking options found warming the bench, it's the latter that is the main concern.