Alongside much-coveted defender Jarrad Branthwaite, Onana is seen as another Toffees man who could leave for big money this summer in order to alleviate Everton's financial crisis.
Sean Dyche's men were previously docked an unprecedented 10 points for breaching Profit and Sustainability Rules, although their penalty was reduced to a six-point deduction upon appeal.
Thanks to Nottingham Forest's own economic indiscretions and subsequent four-point deduction, Everton are safe in 16th place for the time being, albeit with just a four-point lead over the Tricky Trees with a game in hand.
The Toffees therefore remain at serious risk of a first-ever relegation from the Premier League, and such a disastrous scenario would likely force the Merseyside club to entertain lowball offers for their in-demand stars.
Twenty-two-year-old midfielder Onana would be expected to bid farewell should Everton suffer demotion to the Championship, but his contract is not due to expire until 2027, and the Toffees are reportedly holding out for a fee of around £80m in spite of their predicament.
That eight-figure price tag would prove too steep for Barcelona to cough up amid their volatile financial situation, but according to Sport - via TEAMtalk - the Blaugrana could try to sweeten the deal by including some out-of-favour troops.
Sergino Dest, Clement Lenglet, Ansu Fati - who are all on loan elsewhere - and Fermin Lopez could supposedly be offered to the Premier League strugglers, as none of them appears to have a future with Barcelona.
Once heralded as the heir to Lionel Messi, Fati's development has since been stunted by a series of injuries, and he has made just three top-flight starts for Brighton & Hove Albion during his current loan spell.
Lenglet, meanwhile, is now in his second spell in England with Aston Villa, and after not playing a single minute of Premier League football before December 17, he has started each of the Lions' last 12 games in the top flight.
Out-of-favour right-back Dest failed to reignite his career during a loan spell with AC Milan, but he has thrived back in his country of birth with PSV Eindhoven, scoring two goals and setting up six more in 33 games.
Barcelona's hopes of including Dest in a deal for Onana could be scuppered, though, as PSV possess the option to sign the USA international on a permanent basis at the end of the season.
Finally, 20-year-old midfielder Lopez is beginning to make waves in the first team and has scored in each of his last two appearances against Napoli and Atletico Madrid, but he could be bumped down the pecking order by the arrival of Onana or another lynchpin this summer.
While it is ultimately down to Barcelona and Everton to strike an agreement, Onana is reportedly intrigued by the prospect of playing for the reigning Spanish champions and has earmarked them as one of his most desired destinations.
However, the former Lille man is not putting all his eggs in one Blaugrana basket and will listen to offers from other potential suitors, two of whom are said to be Arsenal and Manchester United.