The Saracens fly-half, who is the top scorer in this year's competition with 43 points, picked up the injury in the 23-13 win over France last weekend.
Coach Stuart Lancaster told reporters: "Tom has been seen by a specialist, played back-to-back games and played 80 minutes at the weekend and did extremely well.
"In consultation with the medical teams and [Leicester director of rugby] Richard Cockerill, we've brought him back into the camp. He's available for Italy and Wales."
Lancaster also hopes to have Farrell available for the March 16 trip to Cardiff, where England could secure the trophy and a Grand Slam in the process.