Ian Elliott is head coach for the City of Coventry Water Polo teams, which compete at the highest national and European levels.
He said the teams were "under threat" from the proposed pool changes.
Coventry City Council said it was considering the inclusion of a 50m pool in its new site proposal.
Ed Ruane, cabinet member for sport at the council, said the current facility costs Â£2,000 a day to run.
The council believes the existing Fairfax Street sport centre is no longer fit for purpose. Instead it is proposing a new 25m water park.
Mr Elliott said the city's teams had been "supported strongly by Coventry City Council" but did not want to lose the current pool, which "is ideal for water polo".
The pool is home to water polo teams for youths and seniors of both sexes.
They currently have two girls in the academy GB squad and six youths in British water polo regional training.
Charlotte Noble, goalkeeper for the ladies team, said: "Hopefully people can realise how important the pool is to us."
Water polo is just one of the activities that could be affected by the pool closure.
Earl Radtschenko, 17, from Coventry, is a swimmer who hopes to represent Britain in the Rio Olympics.
He said: "I believe the desire to succeed comes from within, but having a 50m pool and an Olympic coach in Coventry has certainly helped."
Adam Ruckwood, the City of Coventry Swimming Club's head coach and a former Olympian, said some swimmers would have to leave the club if the facility closed, "which would be an absolute tragedy".

The Langholm-based firm is charged with falsely claiming scarves were 100% cashmere on two occasions in 2014.
The alleged offences are said to have taken place at the company's store in Church Place, Dumfries.
Edinburgh Woollen Mill has denied the charge, brought under the Textile Products Regulations 2012.
A trial began at Dumfries Sheriff Court earlier this year and it heard from defence witness Dr Philip Greaves this week.
The textile fibre analyst tested samples of the red and blue scarves at his own facility and found them to be 96.7% and 97.2% cashmere, he told the court.
He said EU and UK standards allow for a 5% tolerance when labelling products.
Asked by defence QC Susan Duff if his findings would allow the scarves to labelled as 100% cashmere, he said: "In terms of regulations, yes.
"There's an industry expression: commercially pure."
Dr Greaves, described as a "world leader" on the subject, said other materials found in the scarves were "inadvertent impurities" which can become part of the product during manufacturing or packaging.
He said: "A block of steel will remain pure but textiles pick up material along the way, and that's why there's a tolerance of certain percentages."
When asked about the results of tests from other labs which found the scarves to contain only 84.4% and 61.6% cashmere, Dr Greaves said bleaching of materials can make them hard to identify as cashmere.
"I think that they perhaps did not recognise the bleached cashmere fibres," he said.
Questioned by fiscal depute Alison Herald about the other examiners, Dr Greaves said: "There's nothing to suggest that they are not skilled but perhaps they are not experienced in fibre damage and this particular bleaching of cashmere."
A second defence witness, Mary Lunn, who tests Edinburgh Woollen Mill fibres for TFT Ilkley, told the court her examination of the scarves found them to be both 100% cashmere.
Asked about the difference with Dr Greaves, she said: "That's within the acceptable range, I would say."
Questioned by Ms Duff on the two lower cashmere results, Ms Lunn said: "Obviously they haven't done it right, in my opinion.
"There's no way there could be that much variation, 2% to 4% maybe, but not that much."
The trial continues.
The closure of the only 50m swimming pool in the West Midlands, could threaten the future of a successful Coventry sport, a coach has said.
[NEXT_CONCEPT]
Edinburgh Woollen Mill scarves claimed to have been mislabelled were correctly marked as 100% cashmere, a testing expert has told a court.