Manchester United led twice at Poland's Tarczynski Arena through Harry Maguire and Patrick Dorgu, either side of a Samuel Chukwueze equaliser, before AC Milan struck three times in the final 35 minutes through Alphadjo Cissé, Gonçalo Ramos and former Chelsea midfielder Ruben Loftus-Cheek to condemn United to just their second defeat in six pre-season matches this summer.
The result followed an opening loss to Wrexham, before wins over Rosenborg and Atlético Madrid, a draw with Champions League holders Paris Saint-Germain, and a penalty shootout win over Leeds United after a 1-1 draw in normal time.
"I think, as a whole, it's been very good," Carrick told MUTV after the Milan game. "I think there are a lot of positives to take from it.
"I think a lot of the performances, the group's grown and got stronger. So overall, I think it's been positive barring today, we're disappointed with today. We didn't play well today, so there's reasons for that. We need to learn from it. We need to improve.
"Some of the boys playing some of their first minutes, there are different reasons, no excuses, we just didn't play very well today. But on the whole, we're ready for next week. I think a lot of the boys will be better for the minutes and, as I say, we've done a lot of work on the training pitch. I think the performances in the games have been pretty good, so we're still in good spirits going into next week."
Kobbie Mainoo, Lisandro MartĂnez and Marcus Rashford all made their first pre-season appearances as second-half substitutes against Milan, having been among the last of United's players to report back following their international summers, while captain Bruno Fernandes, Senne Lammens, Maguire, Luke Shaw and Youri Tielemans all played the full 90 minutes.
United's pre-season took in fixtures across Finland, Norway, Sweden, the Republic of Ireland and Poland.
United begin their Premier League campaign away at Hull City next Saturday, with Carrick outlining his plans for the final week of preparation.
"We've got a good squad, so there are decisions to be made," he said. "We've got a good week's training this week as well to get some more work in. So we'll be ready for next week. I think there's a whole different feeling when it's the first league game of the season, and we'll be there."
He added that his squad would have Sunday off before returning for "five days of training in different ways" at Carrington.
"Sometimes it's a little bit harder, sometimes it's a little bit more of a recovery session. But we'll work through the week and be better for it. I think we look forward to it again. Having a whole squad back home, back at Carrington, and looking forward to the start."