(Adds detail, Ecclestone lawyer, context)
By Andreas Kröner and Jörn Poltz
MUNICH, Germany Aug 8 (Reuters) - German bank BayernLB said on Friday it had rejected a 25 million euro settlement offer from Formula One boss Bernie Ecclestone relating to his involvement in the 2005 sale of its stake in the motor racing business.
State-backed BayernLB claims Ecclestone collected unjustified commissions and undervalued its stake in the motor racing business when private equity fund CVC became Formula One's largest shareholder eight years ago.
"BayernLB has rejected Mr Ecclestone's settlement offer," a spokesman for the public-sector lender told Reuters.
Ecclestone's lawyer in Munich, Norbert Scharf, declined to comment.
Following the rejection, which would have required BayernLB to drop all charges against the 83-year-old British billionaire, one option could be for the bank to negotiate another sum with Ecclestone. It could also launch civil proceedings against him.
BayernLB had originally demanded up to $400 million from Ecclestone, according to financial sources. But during a bribery court case against Ecclestone the public prosecutor and several witnesses said the bank had got a good price when it sold its stake in Formula One to CVC.
In February, a British judge dismissed claims for damages by German company Constantin Medien, which had alleged that Ecclestone was part of a "corrupt bargain" with a German banker to undervalue Formula One and favour the sale of a controlling stake to private equity fund CVC.
Constantin, a former Formula One owner, is sticking to its demand for $171 million from Ecclestone. It claims it would have been entitled to a bigger payment if BayernLB had sold its stake for a higher price.
On Tuesday a German court halted a bribery trial against Ecclestone in exchange for his paying a $100 million fee. He is considered innocent under German law following the settlement.
In 2012 a Munich court jailed Gerhard Gribkowsky, former chief risk officer at BayernLB, for tax evasion and bribery for taking a $44 million payment from Ecclestone and his family trust after the sale. (Writing by Michelle Martin in Berlin; Editing by Arno Schuetze and Noah Barkin)