The Red Devils midfielder has made just one appearance for the club this season, it was during their 4-1 win over Burton Albion in the Carabao Cup on 21 September and his last involvement with a match day squad was their 1-0 win over Southampton two days later on 23 September.
It was initially reported to be a calf injury that kept Carrick out of action, but according to the Mirror, it is a mystery illness that has left even the United medical staff dumfounded. They were unable to explain the illness which caused the midfielder dizziness while playing.
The Portuguese coach will be hoping that Carrick will be available at the earliest as he is facing a shortage in midfield with his two key players Marouane Fellaini and Paul Pogba out injured. Nemanja Matic and Ander Herrera have been deployed in recent games, but they have not been as effective as if one of the aforementioned three were in the lineup.
The Manchester Evening News reports that the England international has returned to training this week, but he remained away from the main group of players, who were preparing for United's Champions League clash against Benfica on Tuesday (31 October). It remains to be seen if he will be passed fit for the Red Devils' game against Chelsea on Sunday (5 October).
The report claims that Fellaini is not too far from returning to action after suffering an injury while on international duty. However, Pogba's return date still remains a mystery after Mourinho admitted that he had no idea about the Frenchman's progress on his hamstring injury. Zlatan Ibrahimovic and Marcos Rojo remain long-term absentees with the former slated for a return mid-way through November.