The invention relates to an apparatus for sealing off a part of a wall (5) in a section (6) drilled into an earth formation and to be placed in such section (6), where said apparatus comprises elongate members (1) arranged along a closed curve, where adjacent elongate members (1) are connected via intermediate links (2), each link (2) being moveable from an unlocked position to a locked position. The invention further relates to a method for applying such an apparatus comprising the steps of:—positioning an apparatus in collapsed configuration in a section (6) drilled into an earth formation with a the wall (5) to be sealed off;—expanding a net or cage in the apparatus, which net or cage is formed by elongate members (1) connected by intermediate links (2);—expanding a flexible member (3) arranged at an outer diameter of the apparatus to seal against the wall (5).