France Under-19 defender Steven Moreira has signed his first professional contract with Ligue 1 club Rennes.
Montpellier coach Jean Fernandez has resigned after overseeing a run of seven Ligue 1 games without victory.
The defender has had previous loan spells at Barnet, Shewsbury, Aldershot and Cheltenham.
McInnes moved into the transfer market after Clark Robertson and Russell Anderson were taken off with minor injuries during the midweek friendly defeat at Peterhead.
McInnes told the club's official website: "With the current defensive injury situation, I'm delighted to have been able to bring in Michael, who is a big strong lad who comes with a good pedigree.
"Michael's arrival concludes things as far as players coming in is concerned while we are looking at loan deals going the other way for one or two of our younger lads."
Hector later played the first 65 minutes as Aberdeen beat Dutch side FC Twente 2-0 in a Pittodrie friendly on Friday night.
Niall McGinn and Peter Pawlett netted the goals in a 10-minute spell early in the second half.
Robertson also started in the back four but Anderson was missing.