I don't think he was great today, but I do think that's an unfair criticism.
One thing I noticed was that when we lost the ball in attacking areas he could often be seen sprinting back up to the halfway line - although we generally won it back before it could get anywhere near his part of the pitch, he was cutting off the long pass in behind him while making sure not to play any runners onside. When we won it back, he ran forward again, and when Forest retained the ball he continued tracking back and was quickly joined by our defence.
That's a thankless and unglamorous responsibility that in a lot of ways doesn't play to his strengths, but he kept at it and that's what gave Gvardiol the cover to press forward.
His whole time at the club he's played in front of a load of players who aren't primarily left-backs but who have all done well in the role - that's mostly on the flexibility and intelligence of our defence of course, but there's something to be said for playing behind a winger who'll accept the ball under any pressure and cover for you when you go forward.