Manchester United had traveled to Moldova earlier this week for their UEFA Europa League match against Sheriff Tiraspol.
Man Utd won the game 2-0 after brilliant goals from Jordan Sancho and Cristiano Ronaldo.
Watch Ronaldo’s penalty
Sancho scored the opener at 17 minutes while Ronald sealed the win with a penalty in 44 minutes.
Casemiro who did not start the match was introduced at the second half.
Being left with no pending business at the city, they jetted back to Manchester.
However, 12 players complained about health problems and did not attend training on Friday and on Saturday.
It is not clear where the food poisoning happened because the players took meals at Moldova and on the plane back to Manchester.
United have started an investigation to determine the cause.
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