Stilian Petrov says thwarting his desire to leave is harming him and Celtic - and warned that his side are not good enough to retain the title.
Portsmouth have had bids rejected for the 27-year-old Bulgaria midfielder.
"We have been flat in our matches and, at the moment, we are nowhere near the form that won us the championship last season," he said.
"So if we don't start playing well it will be a very hard season. Of course it has been affecting me and my form."
Celtic have lost three consecutive pre-season matches, the latest a 4-0 humbling by DC United in Washington.
"We are only two weeks away from the start of the league and we don't look as if we can defend our championship," said Petrov. Right now, my form is poor, definitely
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