Jesus and Mendy always seem to link up well on crosses.
Just the presence of him wide left putting in those balls creates space in the middle, the right back has to come out to meet him and it spreads out the back 4. Also he + Sterling have nice interplay around the box with overlaps etc. it creates that movement we lack.
I'd also be very interested in seeing Mendy play with Ferran Torres on the RW, because part of the frustration has been that he's whipped in some excellent balls but where once Sterling would be at the back post, Mahrez is...wherever he hides when the ball goes in. I can see Torres making the back post run and getting those tap ins.
With Mendy the only problem is just if he can maintain concentration for 90 minutes and not give them a big chance. To be honest, against opposition the quality of Olympiakos in a match that's as close to a dead rubber as possible, it probably doesn't matter.