Louis van Gaal has become even more stretched for options as a recent first-team debutant was forced off in the first half of the U21 side's match on Monday
Manchester United's injury list tally now sits at 17 after Donald Love limped off in the club's Under-21 clash with Middlesbrough.
Love, who was given his first-team debut against Sunderland on February 13, was replaced by Sadiq El Fitouri after 37 minutes as the Scot suffered a suspected hamstring injury.
Fellow defender Joe Riley was given only 45 minutes on the pitch, with the 19-year-old expected to be in Louis van Gaal's squad for Wednesday's Premier League match against Watford.
Adnan Januzaj, who had been operating as a lone striker for the U21 side, was hooked early in the second half to preserve what little first-team options Van Gaal has left.
The clash ended 2-1 in favour of the Red Devils, with an Andreas Pereira penalty and a Nathan McGinley own goal sending the U21 side back to the top of the league.
- Goal