* Shares on track for worst day since mid-December 2021

* FY23 constant currency profit skewed towards upper end of guidance

* Sees FY23 FX impact of $230 mln-$250 mln vs prvs view of $175 mln

June 14 (Reuters) - Australian biopharmaceutical giant CSL on Wednesday flagged an exchange rate hit to fiscal 2023 profit and signaled next year's would also be far below analyst forecasts amid "robust" inflation, sending its shares tumbling.

The trading update shows the long-lasting impact of COVID-19 and inflation on Australia's second-largest company which makes most of its profit converting donated blood plasma into treatments for rare diseases.

As COVID restrictions kept people at home from 2020, CSL raised the fees it pays donors, mostly in the U.S. where it has collection centers. But as restrictions eased, inflation drove up living costs, making it harder for the company to lower fees.

On top of that, currency market fluctuations fueled by perceived banking sector instability and interest rate rises aimed at tackling inflation have hammered the U.S. dollar, the currency in which CSL reports profit, in recent months.

CSL said it expected profit excluding some asset revaluations and one-off costs between $2.9 billion and $3 billion in the 2024 financial year, which the Royal Bank of Canada said was below a consensus estimate of $3.5 billion.

For the year to June 30, 2023, the company kept its profit guidance unchanged but raised its "foreign currency headwind" to a range of $230 million and $250 million, from the $175 million estimate it gave in February.

"The inflationary environment in the U.S. is still fairly robust," said CSL Chief Financial Officer Joy Linton on an analyst call.

"It is unlikely that donor fees will ever go back to pre-Covid levels. We're not seeing big demands for wage increases at this stage, but we remain fairly cautious."

Shares of CSL were trading 7% lower by mid-session, their biggest intraday decline since December 2021, against a slightly higher broader market, as analysts lowered their forecasts in line with the company's guidance.

"It's not so much the FY23 guidance that's the problem," said Carl Capolingua, a market analyst with ThinkMarkets Australia.

"The FY24 guidance was a big miss."

Tim Waterer, chief market analyst at KCM Trade, said that even though the company's 2023 profit forecast was unchanged on a constant currency basis, "investors could not look past the potential hit to the bottom line once currency movements are factored in."

(Reporting by Byron Kaye in Sydney and Archishma Iyer in Bengaluru; Editing by Krishna Chandra Eluri and Subhranshu Sahu)