Adds more details throughout, comment

By Lawrence White and Sam Tobin

LONDON, Feb 27 (Reuters) - Barclays BARC.L shares fell on Friday after media reports it and other banks face potential losses related to the collapse of UK mortgage provider Market Financial Solutions Ltd, amid wider concerns about lending standards and the fast-growing market for private finance.

London-based MFS specialised in complex property-backed loans. It had applied for administration after it ran into difficulties, according to previous media reports and court documents seen by Reuters.

Barclays, Santander SAN.MC and Jefferies are among the lenders exposed, Bloomberg reported on Thursday. The banks declined to comment. Jefferies shares trading in the U.S. fell 8% before closing down 3.5% on Thursday.

Investors are on the alert for any sign of deteriorating lending standards and cracks appearing in credit markets, with some of those fears centred on a boom in private credit, in which specialist funds lend directly to companies.

The collapse last year of U.S. auto parts supplier First Brands and auto subprime lender Tricolor heightened those concerns, although traditional banks were among the most exposed.

Barclays shares fell 1.6% by 1235 GMT, underperforming the broader FTSE 100 index .FTSE which rose 0.4%.

'REAL AND SERIOUS CONCERNS'

MFS, based in London's Mayfair, described itself as a specialist provider of buy-to-let mortgage lending and bridging finance, with net assets of 15.9 million pounds and 149 employees as of December 31 2024, according to its most recently filed accounts.

MFS creditors Amber Bridging Limited and Zircon Bridging Limited had separately filed for an administration order against MFS, court documents dated February 24 and reviewed by Reuters show, citing "real and serious concerns about the mismanagement of the company" and entities in its wider MFS Group.

Amber Bridging and Zircon Bridging, cited as creditors of MFS in the court documents, said there were irregularities in payments due to their accounts and applied for independent administrators to be appointed.

MFS Ltd did not immediately respond to a request for comment.

The Times reported Barclays has 600 million pound ($809.70 million) exposure to MFS.

Analysts from Citi said that the figure may warrant some caution, given banks typically sell on some or all of their exposure when arranging such loans.

"Arranging a loan is very different to retaining that risk on B/S (balance sheet)," Citi said.

"Also not clear if/how much could already be provisioned against (if anything)."

($1 = 0.7410 pounds)