The striker's four-year stay at Old Trafford appears to be coming to an end after he managed just 12 league appearances last term, scoring seven goals.
A year earlier he was the Premier League's equal top-scorer.
The Bulgarian, who cost United £30 million when he joined from top-flight rivals Tottenham, wants to see out the final year of his United contract but is fast giving up hope of remaining at Old Trafford.
And the Bulgarian international took to his Facebook page Sunday to voice his frustration.
"The truth is, I love this club, but I am not going to be useful to anyone if I am not playing," said the 31-year-old. "And I want to play, I want to help
"But for unknown reasons it's not going to happen, or my chances will be limited, so it's better for everyone if we say goodbye.
"If not, I am professional and I will keep doing everything I can to help my team and my team-mates, whenever I have opportunity to do so."
Reports have suggested United have put a price tag of £10 million on Berbatov, although the forward said manager Sir Alex Ferguson had told him the figure was half of that amount.
"Because I am tired of speculation, I am telling you this," wrote Berbatov.
"I read the papers and I see they say 10 million pounds is my price. I go and talk with Sir Alex, and he says to me 5 million. So who is telling the truth, what do you think??"
Berbatov has scored 48 league goals at United, helping them to two Premier League titles.
But his Old Trafford future has been in doubt since he was left out of the squad for the 2010-11 Champions League final against Barcelona at Wembley.
Last season he found himself behind Wayne Rooney and young strikers Danny Welbeck and Javier Hernandez in the pecking order, although he did score a hat-trick against Wigan on Boxing Day.