Andrea Pirlo intends to bring his 22-year career to an end when the MLS season finishes this year.
Justin Morrow scored a hat-trick as Toronto FC sealed the Shield by accounting for New York Red Bulls 4-2 on Saturday.
Led by ex-Barcelona and Argentina boss Gerardo Martino, Atlanta made sure of a postseason berth with four regular-season games remaining.
Toronto FC were shocked 2-1 at New England Revolution as they were denied their first Supporters' Shield in MLS on Saturday.
Portland Timbers star Diego Valeri set an MLS record, and Atlanta United did likewise in front of a crowd of 70,425.
A brace from Jozy Altidore helped Toronto to a win over the San Jose Earthquakes, sealing a spot in the MLS play-offs.
Jack Harrison stepped up with an 84th-minute winner to help Patrick Vieira's New York extend their unbeaten streak to five matches.
David Villa has no doubts over his ability to contribute at the international level, citing ambition and desire as vital ingredients.
New York's Jonathan Lewis scored in the fourth minute of stoppage time, while Clint Dempsey converted a 94th-minute penalty for Seattle.