By Mark Trevelyan

RIO DE JANEIRO (Reuters) - The head of Russia's Olympic delegation on Tuesday criticized athletics' governing body for flip-flopping over the eligibility of long-jumper Darya Klishina to compete in Rio, and said he feared her performance will suffer.

When the International Association of Athletics Federations (IAAF) banned Russia's track and field team in June because of state-sponsored doping, it initially held open the door to Klishina because she trains and undergoes drug testing in the United States.

On Saturday she was suspended because of what the IAAF described as new evidence, but on Monday she appealed successfully to the Court of Arbitration for Sport, and is due to take part in the qualifying round later on Tuesday.

Delegation chief Igor Kazikov said it was impossible to understand why the 25-year-old had been given accreditation and a vest number and then abruptly excluded.

"Why is that happening? If you, the international federation, have allowed her in, then let the woman compete, why are you hassling her the whole time?" he said.

Kazikov also questioned why former Olympic champion Yelena Isinbayeva, who he said had lived abroad for five years, was ineligible.

"Some of the decisions that are being taken are inadequate. This one (Klishina) is let in, and then all this fuss starts up again, and that one (Isinbayeva) isn't allowed, even though she's completely clean.

"Why are these things going on? It's impossible to understand."

Asked about the likely impact on Klishina's performance, Kazikov told Reuters: "I think it will probably have an effect because of all this pressure, when someone has to get ready to compete and you're having to deal with this legal complication.

Not everyone is psychologically able to deal with that tension."

But he added: "She will struggle, she will fight, there's no other way."

(Reporting by Mark Trevelyan; Editing by Bill Rigby)