Mancini revealed afterwards the decision had been taken because Johnson is eager to find another club where he would have more first-team opportunities.

The Blues boss revealed there are “two or three options” and did not entirely dismiss the possibility of a loan move.

However, unlike the likes of Emmanuel Adebayor, who he has told will not figure in his plans, Mancini would be happy if Johnson remained with City after the August 31 transfer deadline.

“Adam can have a future here but you should also understand when you are 23 or 24 years old, you want to play,” said Mancini.

“If you are at a top team, you can’t always do that, so I agree, if he wants to, he has to leave.

“But if that happens I will be so sorry because Adam is a good guy.

“He is a different player to the other strikers and wingers and maybe he could be important for us.”

In fact, Mancini was not entirely happy with his lot even though his team began their Premier League title defence in winning form.

For a start he was unhappy at the slack defending that cost City two goals and, for four minutes, threatened a shock Southampton win until Edin Dzeko and Samir Nasri turned the contest on its head.

Even more importantly was the knee injury Sergio Aguero suffered early in the contest, which leaves Mancini a worried man as he awaits the outcome of a scan that will probably not take place until tomorrow.

“I am worried,” said Mancini.

“We don’t know how serious it is because we need to wait maybe two days for the scan.

“But usually the knee is dangerous.

“The injury was so strange because it was not a bad tackle. It was not strong.

“The good thing was that he wanted to try and play. But at the moment we can’t say anything.”

But Aguero was more hopeful over his injury.

Writing on his official Twitter account last night, he said: “The studies I had done revealed there’s no significant injury but it was a very tough blow to my knee.

“Tomorrow, the physicians will evaluate the time it will take for me to recover.

“I have no words to thank for your concern for me and with this much support, I’ll recover faster.

“And I want to congratulate my team mates for their effort in turning this game around. Now more than ever – C´MON @MCFC !!”

After David Silva has missed a penalty against Southampton, Carlos Tevez broke the deadlock just before the break, only for Southampton substitutes Rickie Lambert and Steve Davis to profit from slack City defending.

Ultimately though, it was to no avail.