The injury forced him to miss this month's Australian Open.
He now says "bone bruising" is taking longer to heal than expected.
The Scot, 32, last played at the Davis Cup in November and will now miss tournaments in France and the Netherlands next month.
"I don't want to rush anything or put a timeline on my recovery," said the three-time Grand Slam champion.
"I'm going to listen to my body and step back on the court to compete when the time is right."
He added: "The bone bruising is taking longer to heal that first thought, so I won't be playing in Montpellier or Rotterdam in February."