Initial attempts to free the animal by slathering him in olive oil failed, with his huge behind preventing him from squeezing his way out.
He was finally freed after animal rescue services lifted off the cover and eased his head through the hole.
Locals have nicknamed the squirrel "Olivio" after his oily encounter.
After the ordeal on Friday, an exhausted Olivio was wrapped in a warm towel and fed glucose, local media report.
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Staff at a local animal shelter say Olivio is recovering well and has now moved on to a diet of Christmas nuts.
"He was almost dead," Sabine Gallenberger from the Squirrel Protection Association told German media.
"Now he is eating a lot and sleeps all the time."
The BBC was unable to verify the size of Olivio's behind.

It follows recent controversy over MLAs' expenses.
The Assembly Commission has asked IPSA, the Independent Parliamentary Standards Authority, to update a report on the Stormont system it compiled last year.
The commission held a meeting on Wednesday to discuss the matters raised over the last few days.
There was a public row between the Independent Financial Review Panel, which sets MLAs' allowances, and the Assembly Commission, which administers the expenses system.
The IPSA report of September 2015, which was leaked to BBC Radio Ulster's Nolan Show, called for changes in the way the assembly reviewed expenses claims which had initially been refused.
But the Assembly Commission, which is made up of the Speaker and MLAs from the five biggest parties, has made the point that the report, in its own words, "did not identify any major issues of concern".
The recommendation about the assembly's review procedure is one of a "small number" of recommendations which the assembly authorities say they are acting on.
The changes recommended in the IPSA report are to be added into the MLAs' handbook.
IPSA will examine the new handbook to "quality assure" it before it is approved by the assembly.
In Wednesday's meeting, the commission also confirmed its intention to develop plans for legislation to "strengthen the effectiveness" of the Independent Financial Review Panel.

The Namibian full-backs have been on the fringes of the Premiership side's squad this season, making only two appearances between them.
Botha, 27, has had his time in Devon disrupted by a broken leg and dislocated ankle in November 2014.
McGuigan, 26, was signed as a result of Botha's injury and has scored four tries for the club.
A red squirrel who got stuck halfway through a manhole cover thanks to his curvy hips is recovering after a lengthy rescue operation in Munich.
[NEXT_CONCEPT]
The cross-party body which runs the assembly has asked the Westminster expenses regulator to do some more work reviewing the Stormont expenses system.
[NEXT_CONCEPT]
Exeter Chiefs pair Byron McGuigan and Chrysander Botha will leave Sandy Park in the summer, the club has confirmed.