After completion of round 2, the 16 remaining clubs are drawn into four groups of four in accordance with. Clubs from the same association cannot be drawn into the same group.
Each club plays one home and one away match against each other club in its group. A club does not play more than two home or two away matches in a row and each club plays one home match and one away match on the first and last two matchdays. Three points are awarded for a win, one for a draw, and none for a defeat.
The four group winners and four runners-up of the group stage qualify for the quarter-finals.