But the manager told Manchester United Radio the duo are yet to suffer any setbacks in their recoveries.
"Mikael's actually doing some of his recovery in France," the Reds boss said. "That's not a problem as far as we're concerned because he's such a dedicated professional and he'll get the work done.
"Ben's also coming along fine and he's doing some goalkeeping work now. But we have to be careful with him. The specialist's assessment is that because it was a graft into the knee - he'd injured his cruciate before - we have to stick rigidly to the plan of almost a year out of action."