Rangers travel to Porto in their third Europa League Group G match, with one win and one loss from their opening two games. Porto have lined up in a 4-4-2 double6 formation in their previous two games and will likely do so again.
Rangers could line up in a formation that allows them to switch quickly from a defensive 4-1-4-1 formation to a more attacking 4-3-3 set-up.
The veteran 'keeper has saved Rangers - literally - on multiple occasions since returning to Ibrox and will start in goals for Steven Gerrard's side at the Estadio do Dragao.
Captain has been guilty of one or two howlers recently but won't be dropped. Delivery from free kicks can be vital and will be eager to put his mistake in the lead-up to Hearts' goal in the 1-1 draw last Sunday behind him when he takes to the pitch in Portugal.
Likely one of the first names on Gerrard's team sheet. The former Brighton centre-half is a rock at the back and has struck up a good rapport with all his central defensive partners.
The Swedish defender has been chosen by Gerrard to play in European games and he could come in for Katic against Porto.
Croatian international has looked like a different player this season after settling in (according to Katic) but he will need to be at his best with Brazilian winger Otavio likely to be starting on the right for the Dragons.
Ah, the clock. Makes things tick at the base of midfield and his experience could be vital in the cauldron that is the Estadio do Dragao.
Former Charlton midfielder's energy and eye for goal could be important and he'll likely line up in the centre of the park alongside...
The number 8 has been a key performer this season for the Gers and will likely continue in the engine room alongside Aribo.
The energetic midfielder can be crucial in games like these where a defence-splitting pass or getting into the right position can have a huge outcome in a game. Has been playing in a front three when Rangers are attacking but can drop back into a more defensive-minded right midfield if the Gers need to contain Porto.
Could the former Liverpool winger be handed his first start? A cameo against Hearts at the weekend suggested he might be preferred to Sheyi Ojo, who has blown hot and cold since arriving on loan from Anfield - although he did nab a cracking winner against Feyenoord.
In some ways this could be Gerrard's biggest call. The Colombian international scored against Young Boys in Switzerland last time out and is always liable to turn it on when Rangers need it most. However, with Porto lining up with chief antagoniser Pepe and the experienced Spaniard Ivan Marcano in the middle of a four-man defence, could Jermain Defoe be a wildcard starter to try and get the better of the duo?
The dependable Wes Foderingham would be an adequate replacement if McGregor suffered an injury or was sent off, while Nikola Katic and / or George Edmundson will provide central defensive cover. Andy Halliday could well take a seat on the bench thanks to his versatility while Glen Kamara is a strong candidate for a place in the matchday squad. Andy King could also be involved while Matt Polster has been on the fringes in recent weeks. Ojo will almost certainly be named on the bench if he doesn't start and whichever striker doesn't start will start on the bench.