Kurt Zouma replaces the Spaniard for Chelsea.
Alonso picked up the problem as he warmed up ahead of the Premier League clash at Old Trafford.
Chelsea star Marcos Alonso was injured in the warm-up
He reportedly felt unwell this morning but tried to give it a go, but he was too unwell in the warm up.
Zouma starts in Conte's three-man defence.
Chelsea fans panic on Twitter as Thibaut Courtois ruled out of Man Utd clash Sun, April 16, 2017
Thibaut Courtois has been ruled out of Chelsea's Premier League clash with Manchester United due to an ankle injury, and Blues fans are worried
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Fans react as Thibaut Courtois is ruled out of Chelsea's clash with Man United
Cesar Azpilicueta switches to the wing-back role.
Chelsea take on United looking to restore their seven-point lead at the top of the table.
United are looking to keep up their hopes of a top four finish.