Manchester United's Nemanja Matic is in serious danger of missing the Red Devils' trip to Arsenal on Saturday, after being withdrawn in the second-half of his side's 4-2 win over Watford earlier this week.
The 29-year-old was replaced in the 54th minute of proceedings by Ander Herrera, and his manager Jose Mourinho confirmed after the match that Matic's request to leave the field of play signalled an 'important' injury.
Matic limped off the pitch after failing to see out the second-half, with Manchester Evening News reporting the Serbian international was spotted walking gingerly through the mixed zone at Vicarage Road.
In his post-match press conference Mourinho said: "He's injured but I don't know [the extent]. He told me he needs to come out.
"For Nemanja Matic to tell me he wants to be replaced, he does not do that if it's nothing important. It is muscular."
With the severity of the injury yet to be identified, the 29-year-old is a doubt for the clash with fourth placed Arsenal, as is Marouane Fellaini. The Belgium midfielder missed the trip to Watford after picking up a knock.
With Michael Carrick also recovering from a heart procedure, which has kept him out of action since September, it suggests Herrera is likely to be recalled to the starting lineup to partner Paul Pogba, and fill the void left by three of United's regular central midfielders.
United will not be the only side heading into Saturday's fixture with injury concerns, as Arsene Wenger is set to be without club-record signing Alexandra Lacazette after suffering a groin injury in Arsenal's 5-0 win over Huddersfield on Wednesday.