Cape Town - Manchester United boss Ole Gunnar Solskjaer admits the Red Devils are "many levels" behind the likes of Manchester City and Liverpool.
Solskjaer has conceded United are 'far away' from competing for the top two positions in the Premier League after their 1-1 draw against Huddersfield Town on Sunday.
Poor form meant United were always going to be relying on unlikely results elsewhere if they were to seal Champions League football, but few expected them to come a cropper at the John Smith's Stadium.
Scott McTominay got them off to a fine start in West Yorkshire, but, like so many times this season, United faltered.
An error from the normally dependable Luke Shaw allowed Mbenza to score his first goal in English football and give Town fans an all-to-rare reason to cheer as a challenging campaign edges towards its conclusion.
"Over 90 minutes we weren't good enough, we missed chances to put the game away, created many chances and didn't let them in our half really," Solskjaer told Sky Sports.
"When you go to these places, stadiums full of energy, we knew if we gave them hope they'd be up for it and unfortunately we did so.
"Sometimes it happens, concentration, application, confidence drops, it was just strange how we changed our approach to the game instead of playing simple. We chose difficult options.
"We are where we are for a reason. Over a long season we haven't been good enough to challenge for the Champions League places. It's not come as a surprise, but we hoped to show a better performance today.
"We haven't taken enough points, won enough games, scored enough goals - it’s always difficult when you lose your manager halfway through the season. It's caught up with us a little bit.
"It shows us where we are. We're not living in fantasy land thinking we can catch the top two, we're far away but we shouldn't be speaking about being far off the top four at Manchester United.
"We're many levels [behind] at the moment, that's the size of the challenge, it's a great challenge for us but I'm sure we'll make it.
On who will stay next season, Solskjaer added: "Every performance has an impact on who you want to keep and let go, that's simple."
On whether Alexis Sanchez will play for Man United again, Solskjaer continued: "We'll see how his injury is for now."