The striker will be out of contract at the end of the season, entitling Rangers to offer him a contract despite being under a transfer embargo until 1 September.
Rangers cannot officially sign or register new players until their embargo is lifted, but they can offer a contract to free agents and players can feature in up to three matches as a trialist.
Daly, who scored in United's 3-0 Scottish Cup victory over Rangers, is now likely to hold talks with the Glasgow club over a possible pre-contract agreement.
The 30-year-old is also believed to be a target for several clubs in Europe after a number of impressive performances as captain at Tannadice.
Daly, who can also play at centre-half, has scored 57 goals in 158 appearances for the Tangerines since joining them from Hartlepool in 2007.