BRUSSELS, Nov 28 (Reuters) - EU antitrust regulators have asked Microsoft's rivals whether the U.S. software giant's proposal to unbundle its chat and video app Teams from its Office product is sufficient to address their concerns, according to a questionnaire seen by Reuters.

Microsoft announced its offer in August, a month after the European Commission opened an investigation into its bundling of Office and Teams, following a 2020 complaint by Salesforce-owned Slack, a rival rival workspace messaging app.

The latest questionnaire could indicate that the EU competition watchdog is building up a statement of objections that could be sent to Microsoft early next year, people close to the matter said.

Regulators asked rivals to provide feedback from potential customers on how their services could operate in tandem with Microsoft's services, the pricing of products with and without Teams and eligibility criteria.

In August Microsoft said that Office without Teams would be 2 euros per month cheaper than with Teams. New customers can buy Teams standalone for 5 euros a month.

Asked for comment, Microsoft referred to its August statement saying that the company was committed to finding solutions to address the Commission's concerns.

The EU enforcer also wanted to know whether it was easy for customers to switch to rivals, if network effects potentially block existing competitors or new ones from entering the market and whether cloud products could replace on-premise solutions. (Reporting by Foo Yun Chee Editing by David Goodman)