Ole Gunnar Solskjaer was frustrated by the way Manchester United blew victory at the death and allowed AC Milan to grab a potentially crucial away goal in this Europa League tie

Despite being second best for much of Thursday's last-16 first leg, the Red Devils looked set to head to San Siro next week in the driving seat thanks to teenage substitute Amad Diallo's first goal for the club. 

The 18-year-old became the club's fourth youngest European goalscorer thanks to his superb, improvised header - a fine effort that was cancelled out deep in stoppage time. 

United's soft underbelly from set pieces was exposed when Simon Kjaer met a corner with a header that Dean Henderson will be frustrated not to have kept out as the first leg ended 1-1. 

"We dropped too deep in the box so the structure, there's a yard or two deep from everyone, really," Solskjaer said of the equaliser. 

"Of course you're always disappointed when you concede a goal in that manner. 

"Simon Kjaer is obviously a good player, he makes a good run, he's strong and his marker gets blocked off, so he gets in front of him. 

"Disappointed but then again that can happen. I've been part of a team that's scored in injury time in Europe myself on a set-play. 

"We know we have to travel there and score a goal and win the game, or score two and draw. 

"Of course it makes it more difficult. Always when you concede at home, you're never happy when you do. 

"One minute before full time is also disappointing but we've got to take that on the chin and just travel down there next week and go for it." 

On the impact of the away goal on the round of 16 tie, Solskjaer added: "It makes it harder but it makes us have to go down there and score goals and win the game. 

"That might suit us. It probably will suit us. We're a team that's better when we go forward, more direct. 

"Today we didn't win the ball well enough or in good enough positions to find the counter attacks. 

"We were too slow, we didn't move our feet well enough in our half and they played well, to be fair, as well." 

Solskjaer was annoyed by several aspects of his side's display against depleted Milan, who travelled to England without the likes of Zlatan Ibrahimovic, Theo Hernandez and Ante Rebic. 

The Red Devils boss was without key men of his own, with the absence of Marcus Rashford and Edinson Cavani compounded when Anthony Martial was forced off with a hip issue. 

January signing Diallo replaced the Frenchman at the break and made quite the impression, scoring his first United goal just five minutes after coming on. 

"I think the pass was incredible," Solskjaer said of Bruno Fernandes' quickly-taken free-kick. 

"I think the pass more or less made the goal, the keeper's position as well. The flick is probably the only thing he can do and he should do. 

"But perfect timing, perfect little weight on the flick. Great moment for the kid." 

Milan boss Stefano Pioli was proud of his team's "amazing" spirit at Old Trafford, with Kjaer securing the positive result their performance deserved. 

"We are working to grow and bring Milan back where we belong," said the Rossoneri boss, who was annoyed to see Franck Kessie's early opener ruled out for handball. 

"These are the best games in that sense, so I was happy to face a team like United. 

"It was a great performance and a great result, but we need another perfect performance to qualify against such a strong team. 

"I keep repeating to my players that I'm not coaching a normal group. This an extraordinary group, the lads always give their 100 per cent in every game, they are just incredible. 

"Before the game we would have been very happy with a 1-1 draw. Tonight we know that we could have earned even more after this performance."