Tevez will miss the FA Cup winners' Community Shield clash against Manchester United on Sunday having been granted leave following Argentina's Copa America campaign until Monday.
"I have spoken to him, his phone is working again," joked Mancini, referring to reasons he gave for not being able to contact the player earlier in the summer.
"He was happy and told me he would come back on Monday - everything was normal.
"He was on holiday, there was a mistake. We said he needed to come back on August 5 with Zaba [Pablo Zabaleta] but it was my mistake because I told him come back on August 8.
"Carlos comes back on Monday because he has 21 days after the Copa America."