And he was right.
While many saw his return to Stamford Bridge as being a major indicator the Blues would lift the Premier League trophy once more, the squad's deficiencies eventually restricted them to a third-place finish, reaching the Champions League semi-final in the process.
With plenty of talent throughout defence and midfield, Chelsea's lack of a truly world-class striker proved their downfall.
Can Chelsea still win the Premier League with just Mario Mandzukic and Diego Costa in attack?
Remaining undefeated against any of the top four in the league, it wasn't their form against fellow title contenders that hindered Chelsea's prospects, it was the likes of Sunderland, Aston Villa and Crystal Palace—struggling teams who soaked up pressure before striking a killer blow to take shock victories.
There was progress elsewhere, but the season ended on a bitter note as Chelsea were left counting the cost of failing to punish their opponents.
To remedy that, Mourinho has already been quick to act. Atletico Madrid's Diego Costa is expected to arrive imminently, per ESPN, while the Brazilian-cum-Spaniard could be joined in attack by Bayern Munich's Mario Mandzukic, as reported by Chris Waugh in the Daily Mail.
Indeed, the World Cup may be taking centre stage for the next month or so, but the on-going transfer rumors mean Chelsea have fans will have plenty to be excited about.
Or do they?
On the surface, the potential of two big names arriving at Stamford Bridge will whet the appetite, but where will it leave the Blues' other front men?
The general belief within the media is that Chelsea will be fielding an entirely new front line next term.
Fernando Torres is expected to be the biggest casualty, according to a report by Darren Lewis in the Daily Mirror (via talkSPORT), while Demba Ba's future has been questioned by the Daily Star's Nick Lustig, suggesting he could join Turkish club Besiktas.
Samuel Eto'o's one-year contract will expire shortly, with no sign of a renewal being offered, and the latest surrounding the future of Romelu Lukaku is he will be trading places with Diego Costa at Atletico Madrid, per Simon Johnson in the Evening Standard.
The maths are simple and regardless of the talent they acquire, if Mourinho offloads all four players as suggested, the Chelsea manager could well be placing himself in a weaker position than the one he has endured for the past 12 months.
Diego Costa and Mandzukic have shown their undoubted qualities in recent years, yet to rely on just two front men to carry the club's hopes at home and abroad is a considerable risk.
Suspensions, loss of form or worse, injury, will leave Chelsea looking incredibly weak, especially when considering what their rivals have at their disposal.
It's a similar story on the continent, with many of the leading clubs boasting enviable forward lines.
Mourinho needs to do the same.
The answer isn't in clearing out those players who failed to make a consistent impact last season. It's about finding a formula that allows them to flourish and offer his team something more.
Ba came to Chelsea's rescue at various times in the latter stages of 2013-14, scoring vital goals against Paris Saint-Germian and Liverpool; Torres also showed his pedigree in Europe, scoring five goals in 10 Champions League matches.
Lukaku's youth meant his form ebbed and flowed for Everton, but he offers Chelsea another option and has a proven record of scoring goals in the Premier League when given an opportunity.
Should Diego Costa and Mandzukic arrive, all three strikers cannot remain at Stamford Bridge, so Mourinho must make a choice about who will.
If it's a case of none, we may well be here in 12 months' time discussing yet another season of transition at Stamford Bridge. And even Mourinho will not be able to survive that.
Garry Hayes is Bleacher Report's lead Chelsea correspondent. Follow him on Twitter @garryhayes.