World champions Argentina look to book their place in the last four of the Copa America when they open the knockout stage of the competition against Ecuador at NRG Stadium on Thursday. The Argentines, defending Copa champions and title favourites, enjoyed wins over Canada, Chile and Peru in the group stage where the solidity of Lionel Scaloni’s side was evident throughout. Confident at the back, well organised in midfield and with a constant threat down the flanks and in attack, Argentina still had to work hard for the points against Canada and Chile earning the opportunity to rest their starters for the 2-0 win over Peru on Saturday. There remains a doubt over the fitness of Lionel Messi however, who sat out the win in Miami as he nursed a sore right hamstring. Scaloni said they will assess Messi’s condition after training on Wednesday evening and should the eight-times Ballon d’Or winner not be able to start, there could be an opportunity to see strikers Lautaro Martinez and Julian Alvarez operate as a pair. Although he started on the bench in the first two games, Lautaro is the tournament’s top scorer so far with four goals in three appearances. Curiously, the most recent time that Inter Milan’s Lautaro and Manchester City’s Alvarez started together was against Ecuador in a pre-tournament friendly on June 9th which the ‘Albiceleste’ won 1-0.