The teenage darts ace even recommended the man Ruben Amorim should turn to between the sticks.
Littler shared his frustrations with Onana during United's Europa League clash with Viktoria Plzen.
After a quiet first half, the Red Devils keeper gifted the home side an opener just minutes after the restart.
Onana passed the ball straight to Plzen's Pavel Sulc, who squared for Matej Vydra to stroke the ball into an empty net.
Littler wasted no time reacting on social media as he watched the match from home.
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Sharing a snap to his Instagram story, the Nuke wrote: "Bring back Dave," with a glove emoji in reference to David De Gea.
The former United stopper left Old Trafford in 2023 and is now playing in Italy for Fiorentina.
De Gea spent 12 years in Manchester between 2011 and 2023, making 545 appearances for the club.
He also won eight trophies during that time including a Premier League title.
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After over a year without a club, the Spaniard joined Fiorentina in August and has since been in stunning form.
In 11 appearances for the club, he has kept six clean sheets and conceded just 11 goals.
Fortunately for Onana, substitute Rasmus Hojlund spared his blushes.
The forward came off the bench to equalise for the visitors as he tapped in from close range.
Hojlund then added a second with just two minutes remaining to put his side on course for their first European away win in 20 months.
It also preserved Amorim's record of never losing three consecutive matches during his managerial career.
Ahead of the trip to Czechia, United had been beaten by Arsenal and Nottingham Forest in their last two fixtures.