I just want it to be clear that Wilson has had choices within the current squad. A different manager may have done things very differently, maybe with less success, maybe with more.
Some managers have a preferred formation, playing style and definition of player roles within their team. They will make signings based on their ability to fulfill certain roles in the team.
Other managers like to assess the squad they inherit and add the highest quality players that they can get. They'll pick the eleven players that they think are their best, and then choose the formation, team composition and playing style that they think suit them best.
Let's say the England manager appreciates the pace and dribbling ability of Aaron Lennon on the right wing, but loses him to injury
He may decide to call Theo Walcott into the squad and even use him from the start, knowing that his attributes, similar to Lennon's, are what complements the rest of his first eleven, and vital for his playing style to work. If Walcott is also out he may even turn to the unproven Nathan Dyer to find a similar type.
Or he may perhaps look at who else was already in his squad and replace Lennon with James Milner, who he thinks is a better quality player than both Walcott and Dyer. Or Glen Johnson, who he also rates very highly, and who he knows will make the team more solid defensively, maybe needed against the tricky left winger of England's next opposition.
The options are there, and the manager's choice will be determined by his football philosophy.