FRANKFURT (Reuters) - An extension to Deutsche Bank <DBKGn.DE> supervisory board Chairman Paul Achleitner's contract is not yet a done deal, several shareholders of Germany's flagship lender told Reuters on Friday.

German monthly Manager Magazin reported earlier, citing shareholders, that Achleitner was likely to remain in his post for a second five-year term after his contract runs out in May.

Achleitner has been under pressure from investors who have grown impatient with Deutsche's shrinking earnings and faltering share price.

Manager Magazin said Deutsche's top investors, which include the Qatari royal family and Blackrock <BLK.N>, would rather keep Achleitner in office than have a change in the chairman post at such a critical time for the bank.

Deutsche Bank and Blackrock declined to comment. The Qatari royal family's holding companies were not immediately available for comment.

One shareholder told Reuters that more clarity was needed on how much it would cost Deutsche Bank to settle claims it mis-sold U.S. mortgage-backed securities, on whether the bank will need fresh capital, and what strategy changes may be yet to come.

"We won't just give him our full backing now, when there are still so many outstanding issues," one shareholders said, who declined to be named.

Another investor, who is among Deutsche's 10 biggest shareholders, said: "If the U.S. settlement turns out to be extremely expensive and a possible capital increase is unsuccessful, we won't support Achleitner."

A decision on whether to extend Achleitner's contract will likely come in the spring, ahead of Deutsche's general shareholders' meeting in May, the shareholders said.

Some investors cautioned that it would be difficult to find an alternative to Achleitner.

"Deutsche Bank is in stormy water, you can't just let an amateur have a go," one top-10 investor said.

Sources have told Reuters in the past that former Bundesbank chief Axel Weber, who is now chairman of Swiss bank UBS <UBSG.S>, was seen as a possible candidate to succeed Achleitner but that he had indicated he was not interested in the job.

(Reporting by Kathrin Jones and Andreas Kroener; Additional reporting by Christoph Steitz and Edward Taylor; Writing by Maria Sheahan; Editing by Mark Potter)