Lawes and McGuigan withdraw from England's Six Nations squad
Lawes, who was named as a vice-captain in the squad, withdrew due to a calf injury after he limped off during Northampton Saints' clash with La Rochelle while McGuigan injured his knee.
"Tom Dunn and David Ribbans have been called up to the squad by head coach Steve Borthwick," the RFU said in a statement.
England begin their Six Nations campaign against Scotland at Twickenham on February 4.
The injuries give new coach Borthwick a selection headache with fellow hooker Luke Cowan-Dickie set to miss the start of the Six Nations due to an ankle injury that requires surgery.
Jamie George suffered a concussion when Saracens played Edinburgh in the Champions Cup on Sunday.
George sustained the injury in a tackle and could be stood down for 12 days as per World Rugby protocol, meaning he may not train until the day before the Scotland game.
