The Torino boss' mood was not helped by a 2-0 away defeat in Serie A, with Lopez not included in his plans, despite star striker Andrea Belotti's absence through suspension.
Mihajlovic, who had discussed the situation ahead of the match, was asked to address it again after the game and suggested the Argentine's omission could become permanent if he does not trim down.
"We have been trying for months to get Maxi Lopez to lose weight," he said to Rai.
"If a player wants to be in my team, he has to respect the rules. Until he can do that, he will not be called up."
Mihajlovic had already criticised Lopez in September, slamming the 32-year-old for being seven kilos overweight "which is like having a washing machine on his back", ordering him to change his diet and threatening to fine him if he did not show progress.
But before the Bologna game, he explained his move to drop Lopez by saying: "It is because the washing machine is still there."
Reports in Italy suggest Mihajlovic is desperate to sell Lopez before the transfer window closes.
Lopez has scored once in 10 appearances in all competitions for Torino this season and has been an unused substitute on a further 18 occasions.