The Russian, 29, tested positive for meldonium at January's Australian Open.
When asked if Sharapova would play any more tournaments, Shamil Tarpishchev told R-Sport news agency it was "very doubtful" and added the five-time Grand Slam winner was in a "bad situation".
In March, Sharapova said she was "determined to play tennis again".
The International Tennis Federation (ITF) provisionally suspended Sharapova on 12 March.
She is waiting to hear the full extent of her punishment, which could be as much as a four-year ban, although experts say a six-month or 12-month suspension is more likely.
That is because the World Anti-Doping Association (Wada) admitted in April that scientists were unsure how long meldonium stayed in the system.
It even suggested athletes who tested positive for the substance before 1 March could avoid bans, provided they had stopped taking it before 1 January.
However, Sharapova has already admitted she continued taking meldonium past that date, saying she was unaware it had been added to the banned list as she knew it by another name - mildronate.
We've launched a new BBC Sport newsletter ahead of the Euros and Olympics, bringing all the best stories, features and video right to your inbox. You can sign up here.

This is basic economics. As the rig count of American production picks up, according to the most recent data published this week, there's an expectation that production will rise, supply increase, and the price subsides.
There are shorter term fluctuations.  Wednesday's trading has been affected by Saudi Arabia confirming it is cutting supply to Asian customers, in line with its commitment last month to the wider cut in production by the OPEC exporters cartel.
But the trend of recent weeks has anticipated the growth in output.  And we learned from energy analysts Wood Mackenzie on Wednesday that it foresees the Texas fields of the Permian Basin to the main player as the frackers return to work. Further south, there are shale developments moving ahead in Argentina.
WoodMac, based in Edinburgh, forecasts investment is going to pick up more widely this year, for the first time since 2014.  Oil companies, which have been holding back from committing to big projects while the price has been low, are showing signs of changing that.
This is not only because of a much higher price than this time last year, but also because costs have been slashed over the past couple of years - by an average 20% for each of the past two years.
That process is running out of the opportunities to keep cutting, but exploration and production spend is set to rise to $450bn, the forecast suggests. That's a 3% rise, but it's still 40% below 2014.
Areas to watch include 'tight oil', including fracking - up by a forecast 23% in the US, to $61 billion, and potentially boosted by the Trump administration's enthusiasm for energy security and scepticism about climate change.
Final investment decisions on major projects reached 40 in 2014, and fell to nine last year.  The forecast is for 20 this year, most of these smaller projects building incrementally on existing infrastructure, with much higher return on investment than in the boom times of only three years ago.
Deepwater drilling may get more attention, but half of the existing big deepwater projects are reckoned to break even at more than $60, so they are looking doubtful for the foreseeable.
Among the regions worth watching, the North Sea does not feature, but Norway's northern Barents Sea is worth watching, including an area in which there's a dispute with Russia.
That's while the ethical watchdogs who police Norway's vast state oil fund have served warning that they're going after industries which are the worst polluters.
The fund owns around 2% of the world's stock market valuation, and it is widely seen as providing a lead on ethical investments. So a fund sourced from oil and gas revenues and profits is now turning against those who burn the stuff irresponsibly.
Former world number one Maria Sharapova may never play again following her failed drugs test, the president of the Russian Tennis Federation says.
[NEXT_CONCEPT]
Being upbeat on investment means being downbeat on prices, or at least that's the way it is with the oil industry.