Rooney broke the fourth metatarsal in his right foot during Manchester United's 3-0 defeat by Chelsea yesterday, sparking fears he could miss the entire tournament which begins in 40 days.
"Wayne is young and has a good team around him. The main thing is he mustn't do any hard-impact exercise," Roberton told BBC Radio Five Live's Sportsweek programme.
"It's better for him to swim. Being young it can take between four and six weeks for this injury to repair properly.
"He must build up gradually the amount of exercise he does and have rest days between sessions. When running 40 or 50% of the body's weight is put on the metatarsal's head.
"He should rest and not do much exercise and should be back to normal in four to six weeks.
"I would doubt very much if he could make the first game, or even the second, of the group stages. I would say he can be back in seven weeks. I would build up between four and five weeks."Reuse content