Everton v Manchester United
Live on BBC One
Defensive headaches for Martinez
Everton's midweek performance at Anfield was so horrendous that the 4-0 defeat actually flattered them - it could have been so much worse. The Toffees desperately need a victory at Wembley here to save their season - and perhaps to save Roberto Martinez's job.
The primary reason for Everton's awful performance was poor defending. This has evidently been a clear weakness throughout this season, and throughout Martinez's reign, but they weren't helped by the injury absences of captain Phil Jagielka and right-back Seamus Coleman.
To make matters even worse, Ramiro Fuenes Mori was dismissed for a terrible tackle on Divock Origi, and centre-back partner John Stones departed through injury. Everton played the latter stages with central midfield duo James McCarthy and Mohamed Besic deputising at centre-back.
Stones will probably be fit to start here, but Fuenes Mori's suspension gives Martinez a serious headache. Using Gareth Barry in his old position as a left-sided centre-back seems the most obvious solution, with Besic another option.
Either way, Martinez will surely ask his central midfielders, probably Besic and McCarthy, to remain extremely deep and protect a nervous centre-back combination.
United well set to pounce on uncertainty
That's particularly crucial considering the system Louis van Gaal has deployed in Manchester United's last two matches, an attack-minded 4-1-4-1 system featuring Anthony Martial, Wayne Rooney, Juan Mata and Jesse Lingard all behind Marcus Rashford.
Rooney and Mata playing together in that zone is particularly intriguing, particularly as both are capable of popping up in the opposition box to provide goals and assists. Everton's makeshift defensive structure will be given a stern test.
Martial, meanwhile, will fancy his chances of causing Bryan Oviedo problems. The Costa Rican is yet another playing in an unfamiliar role because of Coleman's injury, and he made a poor mistake for Liverpool's opener on Wednesday. Accustomed to playing on the left flank, Oviedo looks entirely uncomfortable on the right.
The opposite flank will see Lingard tracking Leighton Baines back, although he'll also look to dart inside into space between the lines. Baines hasn't been at his best since his long injury lay-off, and this is yet another area where United might find some joy.
Everton's area of strength, of course, is going forward. Don't expect much attacking flair from Tom Cleverley against his old club - he'll probably be pushed back from his narrow left-sided position by the overlapping runs of Antonio Valencia.
Expect goalmouth action
However, Aaron Lennon has looked lively in recent weeks, and could cause Timothy Fosu-Mensah problems. The young Dutch defender has performed impressively since coming into the side, and is an old-school defender who loves making tackles. It will be interesting to see where Lennon positions himself - he's become a more intelligent player since moving to Goodison Park.
Ross Barkley and Romelu Lukaku remains a dangerous attacking partnership, and Everton's main gameplan might be about transferring the ball forward to them as quickly as possible.
Barkley might relish playing against a sole defensive midfielder, probably Morgan Schneiderlin, as he'll find space in the channels. Lukaku, meanwhile, will probably play in an inside-left position up against Daley Blind, although the Dutchman performed superbly against the big Belgian in the recent league meeting.
There should be goals here, as both teams have promising attacking combinations on show, but United are so much more solid defensively. It's tough to see Everton coping at the back, which makes Van Gaal's side strong favourites to qualify for the final.