The Chilean manager admits their much-hyped opponents boast various attacking threats.
La Liga's stranglehold over Europe's cup competitions makes the pair's task unenviable.
Real Madrid host Manchester City on Wednesday after a 0-0 in the Champions League first leg semi-final.
Daily Mail claimed that United were ready to pay up to £70m to secure his services.
Vincent Kompany, Kevin de Bruyne and Sergio Aguero were also involved after being rested at Southampton.
The out-of-contract veteran believes Champions League qualification remains an attainable.
Barcelona keeper has been heavily linked with a move to Manchester City in recent weeks.
Casemiro suffered a knock during the weekend victory over Real Sociedad.
Manuel Pellegrini's side face tricky task against 10-time European Champions in Spain. Find out where to watch the match live in the UK.
Claudio Ranieri's table-topping team have put the Premier League's traditional big four to shame.
The forward scored the Gunners' winning goal during their weekend victory against Norwich City.
Portugal forward likely to start against Manuel Pellegrini's side in Champions League semi-final decider.
Liverpool were also humbled by Swansea, who secured their Premier League status with victory.
Southampton face Manchester City in a Premier League clash on Saturday. Find out how to follow the match in the UK.
Real Madrid visit Real Sociedad only four days before their Champions League encounter with City.
Samir Nasri is ready to return to the squad for the trip to Southampton.
Leicester City are in with a chance of securing the Premier League title.
The duo are expected to miss the trip to Real Sociedad on Saturday.
Portugal star rated doubtful for Champions League semi-final second leg showdown in Spain.
Louis van Gaal has one year left on his contract at Manchester United.
The Blues also retained the Uefa Youth League title this month.
Sport claims that Chelsea and Manchester City are also interested in the Brazilian.