United drew 1-1 with already-relegated Huddersfield on Sunday meaning they are now four points off the Champions League places.
And with just one game remaining this season, it means Manchester United will not play in Europe’s elite competition next season.
Mata posts a weekly blog on his website, generally summarising the mood of the United team for the week.
But the Spaniard kept his message short and simple when posting his update on Monday.
Mata simply wrote: “You deserve better. No more words needed.”
Manchester United will now be in the Europa League next season.
It’s a competition they won under Jose Mourinho in 2017 with Chelsea and Arsenal both in the semi-finals this season.
And United boss Ole Gunnar Solskjaer wants to take inspiration from the two London clubs next season.
He said: “You can sometimes use the Europa League as something positive, as Chelsea and Arsenal have done this year, as we did a couple of years ago when we won the Europa League.
“I am an optimist by nature and I will make the most of it.
“The kids will get chances to play games, that’s for sure.
“We’ll have to make something positive out of it, no matter what.
“We gave ourselves hope and belief that we could make it [Champions League qualification] and we have had other results [go for us] but we’ve not been able to capitalise.
“It’s a big blow.
“Of course everyone is disappointed in the dressing room and you could say we lost the opportunity today for Champions League football, but that’s not the case, it’s been all through the season that it’s not been good enough.
“We haven’t been able to turn games to our advantage when we should have done, like today.”