Although Rostov had occasional excursions over the halfway line the game was quickly turning into a contest between United's attacking ideas and their opponents' packed defence.
Marcus Rashford started as striker in United's 1-0 defeat to Chelsea in the FA Cup quarter-finals at Stamford Bridge on Monday night, despite suffering from a bout of illness.
Anthony Martial and Wayne Rooney will not figure in the return against Rostov, with the tie in the balance after the first leg ended 1-1.
He admits that at Manchester United the players are always striving to achieve greater things but believes it is important that they take one stage at a time before thinking about winning the competition now. So he is out of my mind.
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"We had one gift and we thought one gift was enough", Mourinho said. "It was some kick in his knee area so he can't even come out to the pitch". Manchester United's presence back in the competition would help establish them as a big European force once again, and to do that, they simply must win the Europa League.
Zlatan Ibrahimovic was playing again, but he'll be sidelined through suspension for the next two Premier League matches, as will Ander Herrera.
Sergio Romero came to United's rescue in the 78th minute, as the shot-stopper produced a stunning save to keep out Aleksandr Bukharov's glancing header. They have not won a single match in their last five European away matches, but they are in their first ever round of 16 and a couple of away goals could be all they need to secure an upset.
What time does it start?
FC Rostov might have been underdogs for their Europa League second-leg meeting with Manchester United, but this still felt odd. The 1-0 win at Old Trafford was otherwise a tepid affair, which they controlled for long spells but in which they failed to take charge on the scoreboard.
Ibrahimovic is back in so they'll have plenty of belief and he's probably got the anger out of his system by now.
With the quality of the pitch woefully lacking, it was hard for either side to have any sort of passing game, but United were able to start with a few good chances early on from Ibrahimovic and Mkhitaryan.