The Tangerines are currently on a pre-season tour of Germany but Ryan is unlikely to be involved in the season opener against Partick Thistle next month.
The 28-year-old appeared 29 times for United last season after arriving from Sligo Rovers at the beginning of last year.
"I have told Richie it's going to be difficult for him to get into the team," he told the Dundee Courier.
"I could keep him as cover but that's not fair because he needs to be playing football.
"There is nothing happening yet but I am hoping we get something sorted with him soon. We are well covered in midfield and have youngsters coming through."