He is a shrewd operator who doesn't leave anything to chance and doesn't like to give anything away. He is miserable and tight as a manager and that is no bad thing.
You might even say he has a bit of Walter Smith about him. Those traits were certainly in evidence at Pittodrie on Thursday night when his Aberdeen team played out a cagey goalless first-leg draw against Groningen in Europa League qualifying. Both teams were so respectful of each other it wasn't true.
Only the result of Thursday's second leg will determine whether he has got his calculations right. Aberdeen can attack sometimes but I know what McInnes and his assistant Tony Docherty are like. They won a lot of games 1-0 last season and their mentality seems to be that while it is great if you win games by two or three goals, the main thing is simply to get the win.
The way they see it, if you are leading narrowly after 75 minutes then you are better to see it out with four centre-halves across your back line, a solid midfield in front of them and look for chances on the break with the pace of Niall McGinn and Peter Pawlett.
That approach may mean they are better equipped for the away game in Groningen. They are certainly still in the tie, because the big advantage was not losing that away goal. Aberdeen got some great results away from home against Celtic and other good teams last season, so they are all set up to go there and get something. If they can defend well, and nick a goal, then that might be enough to knock this Dutch team out. Then, tactically, Derek would have been spot on last Thursday night, by being what I would say was over-cautious.
But it could just as easily backfire on them, too. While Groningen never looked like scoring they were probably waiting for Aberdeen to come out and play, and were surprised that they never really did. This time, they could come out and have a go, score a few goals, and leave Derek thinking: "I wish we'd had more of a go at them at our place". That is how delicately balanced the tie is.
One thing was crystal clear though: Aberdeen fans believe in Derek McInnes now. There is a huge difference in the way the fans stayed with the team right through that game, even though it was quite a boring match with not much happening. Previous managers at 0-0 against Groningen at home, with their team not really attacking, would have got a bit of stick. But Derek has earned the right to do what he wants.
Big summer signing David Goodwillie only came off the bench but I am convinced that picking him up for a year is an excellent bit of business. Quite simply, if he can get himself right, they are getting a top player. I know David from working with him at Dundee United when he was a youngster.
He needs to find the right club, and I think Aberdeen could be that club. There might be a realisation on his part that he has to get his career back on track. While Aberdeen are lucky to have a player of his calibre, I also think he is lucky to be at a club like this. He is at a crossroads now and I think Aberdeen will be the beneficiaries of that. Docherty was with him at United and knows he is a good lad if you handle him properly.
Derek is perfect for him as a manager - he won't let him off the hook, but will manage him correctly, and treat him like an adult. Getting him for a year, which sends out the message that it is easy for the club to let him go if it doesn't work, could be an unbelievable bit of business.
It was a bit of a mixed bag for Scottish teams in Europe last week. I was in Iceland to watch Celtic against KR Reykjavik and will be back there on Thursday to see Motherwell.
It was job done for Celtic, although they should have won by more in a match which was almost like a pre-season game, and they should win comfortably at Murrayfield on Tuesday night. St Johnstone had another good result in drawing away to Lucerne in Switzerland, while Motherwell could still go through, although you have to say drawing 2-2 at home after taking a 2-0 lead against Stjarnan was the poorest effort of the bunch.
I have been there myself - we had a nightmare against Mypa with Dundee United when two late goals gave the Finnish side a 2-2 draw to knock us out - but it is about time Scottish teams started coming out on top of these evenly matched games. We would reap the benefits for years to come.
With Real Sociedad waiting in the next round - they have France World Cup star Antoine Griezmann and have just signed one-time Celtic target Alfred Finnbogason - I would be amazed if Aberdeen can make it all the way to the group stage.
But if you are to go out of Europe you want it to be against one of the Continent's bigger teams, not by slipping up against one of the minnows. I still think all four Scottish teams can get through next week, but at this moment I would take three out of four.