Although I haven't seen links to specific CBs, there's been a lot of talk that Mourinho will buy at least 1 CB. Bailly + x is a fine CB pairing with Smalling, Jones and Rojo as proper cover.
In regards to bombing out of the CL, sure the back line wasn't great in the away fixtures against PSV and Wolfsburg, but they also failed hard on attack, scoring only 7 times in 6 matches against that competition. The biggest failure United had this year was finishing, the attacking targets they're linked to help address that.
I saw a report on United being linked to Lindeloff and to van Djilk. Lindeloff is possible, van Djilk is not, IMO. He's going to go for way more than he's worth.
I'm comfortable with Bailly as long as he stays healthy. I'd want someone a bit more proven than Lindeloff for Champions League to go with him, but if Smalling stays, he's acceptable for now.
Griezmann would transform United. I like his versatility. Where he lines up will depend on who else United buys and if Zlatan comes back for one more season. Griez + Zlatan would be a potent attack, though I would wager that Griez lines up as a 10 behind Zlatan. I don't ever see Mourinho lining up with a 4-4-2. If Zlatan goes, Griez is the out and out striker, and United will either
a. continue to employ Mkhi as the starting 10
b. pay through the nose for Hamez even though I have doubts about him fiting into Mourinho's tactics
c. make a shock bid for a player to be determined
If I'm Atleti I tell Griezmann "Sure. Just know that all interested parties will be referred to your buyout clause. If no one meets that figure we will see you on insert date he's do to preseason here."
First you shouldn't believe every rumor. That's a potential list that probably includes a realistic target or two along with some speculative targets likely drummed up by the press.
As for who United currently have and the potential buys, you have room for two attacking players. There's either upgrading the squad and/or replacing players who are leaving. And you could see players go. Rooney, Mata, Martial... I've seen rumors for Rooney and Martial and Mata's contract is up next Summer.
As for defense I wouldn't be surprised to see a CB signing, but there are also rumors of Smalling leaving so that's one-for-one. They could also be in for more than one.
I recall reports of Mourinho not liking Shaw. Either way, I'd ask yourself if Mendy is an upgrade and then consider the depth chart. Next season will be the CL and so United will definitely need to upgrade the squad and improve their depth. I've seen the figure of 200 million pounds as a transfer budget. Factor in City's rumored 300 million and Chelsea's 200 million and they will likely need to spend that much just to compete domestically much less a run in the CL.
I've read everything you outlined, but you said it yourself, how much is to be believed? Rooney I can definitely see being sold to a lower level English club, China, or the MLS even. How huge would he be for a MLS team? He'd be just a notch below Beckham in terms of hype. He still has something left in the tank and is a United club legend, he's just not a starting 11 player for a club like United anymore.
Selling Martial would be even more stupid than selling Memphis was. I may be in the minority, but if I had to choose between Martial or Rashford, I'd choose Martial. Rashford is a better fit for the EPL, but in terms of overall skill, for my money, I take Martial moving forward. United paid too stupid of a transfer fee to give up on him after just two seasons. Let him settle in a little bit. He's a 20 year old kid who just got divorced. I'm sure that he's been distracted this past season as a result. He needs a nice, long summer off free from Euro or World Cup qualifiers to refocus and get himself back in shape to win a starting 11 spot with United for this year.
Mata I could really go either way on. He was a good soldier and had a great season, but he can be upgraded on for sure. This may be the best time to sell him.
I hadn't seen the reports on Smalling wanting out, where did you read that? In that case, United would need to sign two first team CB's, IMO.
I've also heard the same speculation about Shaw and Mourinho butting heads. Shaw hasn't been healthy since coming to United, but I've also heard whispers of Mourinho not being happy with Shaw in training and with his work rate. It will be interesting to see what happens there, as I think Shaw still has a lot of promise if he can stay healthy. If the above is the case, though, signing Mendy makes a lot of sense.
Re: the EPL transfer budgets. **** China. They ****ed over every other top English team outside of Chelsea by coughing up close to 100 million Euros for Oscar and Ramires. What does Chelsea really need? Diego Costa is a headcase. Unless he requests a transfer and Chelsea need a striker, not much really. I guess they can upgrade on Matic, but what midfielders would really be available that would be upgrades? And no, I don't see Verratti going to England. He's going to Spain or Juventus, IMO.
Perisic, Griezmann, Costa & Hamez are all realistic targets for United; though I'm skeptical about Hamez.
Me too. I just don't see how he would fit on United's squad. He'd be a luxury buy. Have Costa and Perisic played on the right side? I know both of them to be left wingers. Rashford and Martial will likely split time at LM/LW this year.