The 22-year-old moved to the West London outfit for a fee of around £3 million, that could rise to £6m, after failing to agree a new deal with the Citizens.
Sturridge has since proven to be a shrewd acquisition by the Blues after scoring 20 goals and laying on a further seven in his two-and-a-half years at the club.
And Mancini is still ruing the loss of the forward after revealing he questioned Sturridge's motives in the tunnel after a game against Bolton, who Sturridge was loaned to during the second half of last season.
"I asked him last year when he played for Bolton why he left Manchester City and he said he didn’t know,"said the Italian.
"I know [Daniel] Sturridge well, I have watched him many times.
"Given the chance I think I would have liked to have kept him, but now he is at Chelsea we can do nothing. I know for sure he was one of the best young players that was here.
"It was not difficult to see that Sturridge was going to be a good player. It was strange because he started out in Manchester and someone let him out of the club for nothing."
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