The tour operator told customers who contacted them over the weekend that the business was not in trouble and that all of its holidays were protected by UK holiday protection scheme, Atol.
The company also held talks with a range of suppliers to reassure them that it had plenty of resources to cover the summer holiday season.
READ: Thomas Cook shares plunge further as Citigroup cuts rating to 'sell' and slashes target price to 0p
“In the last few days we have had a number of discussions with our suppliers to explain the ample resources we have to continue to do business as well as our strengthening liquidity position,” a Thomas Cook spokesperson said.
Thomas Cook’s market value plummeted 40% on Friday when Citigroup told investors to sell the stock because the shares were worthless.
Citigroup said the company would likely need a debt for equity swap or substantial rights issue.
The broker comments came a day after Thomas Cook posted a record £1.5bn loss for the first half and warned that earnings for the rest of the year would be weaker due to Brexit uncertainty.
Over the weekend, Thomas Cook revealed that it was in talks with a payment provider in the Nordic region to extend the length of time it holds onto customer payments before passing them onto the firm.
Thomas Cook declined to name the card supplier but said it was confident it would reach an “acceptable solution in the coming days”.
In last week's first-half results, Thomas Cook said it had agreed a £300mln bank facility to provide additional liquidity for the winter 2019/20 season, subject to the sale of its airline business.
Citigroup said a highly-priced airline disposal could alleviate near-term pressures and free the way for an offer for the remainder of the business from a non-EU entity such as Chinese group Fosun, which has a 17% stake in Thomas Cook.
In morning trading, shares recovered slightly to rise 1.3% to 11.95p.