Helveg blow for Milan
Helveg has recently been linked with a move to Manchester United, but for the time being is concentrating on getting back to full fitness.
"I started to run on Sunday, but it did not go well," the Danish international told BT.
"The ankle is aching again and it is uncertain when I will play again.
"The longer I am absent the more it affects my match fitness, which obviously just prolongs the time until I am ready."
Meanwhile Milan are rumoured to be watching Zivis Vrysas, but may have to offer owners Perugia players in exchange.
Another new face could be Parma's Sabri Lamouchi, who is a long term target of The Rossoneri.