Some footballers are too versatile for their own good. Philipp Lahm always considered himself a right-sided defender but played almost exclusively at left-back until the age of 25. He's since been transformed again, serving as a midfielder since last fall. Bastian Schweinsteiger also was 25 before he was moved from the wing to his natural, central midfield position.
Thomas Mueller falls into the same category as Lahm and Schweinsteiger as being a player who can put in a good shift in a variety of positions. Such versatility is a great asset to have but often comes at a price.
For Schweinsteiger, that price was spending half his career as a winger who, despite his many merits, was too slow and not skilled enough in attack to be world-class. Once converted to a holding midfield role, he had few peers and was arguably the world's most complete (if not best overall) player in his position.
Lahm has few peers at left-back and is a very good midfielder. Among right-backs, he stands alone. But like Schweinsteiger, he's spent many years as a role-player, filling in at necessary positions not because they best suit him but because he can.
The same can be said of Mueller, who throughout his career has been shuffled from position to position. Until recently he was always a right-winger for Joachim Low's Germany, but when he began his club career under Louis van Gaal, he played in the hole behind a main front man. He's also filled in on the left flank from time to time.
Over the last 12 months, Mueller's role as a footballer has become more uncertain than ever. Per Transfermarkt, Pep Guardiola used him 21 times on the right wing, 15 times as a central attacking midfielder, nine times as a striker and four times on the left wing. The undefined nature of his role, combined with his playing the full 90 minutes in just 23 of his 51 appearances, led to Mueller publicly expressing frustration (via The Guardian) with his situation. He even had doubts as to whether he was part of the club's long-term plans, demanding a meeting with Bayern's higher-ups.
Days later, Muller extended his contract until 2019. It is yet to be revealed whether he was told of a specific position he'd been selected to occupy in the long-term, but his decision to commit to two further years beyond the duration of his previous contract suggests that he'd received the reassurance he desired.
Typically, a well-regarded and valued player is used in a consistent role that is indisputably his; others who are still making their way into favor are fit into the team around certain pillars, playing where they can. Mueller's frustration was therefore understandable: He's almost 25 and has played at a high level for Bayern for the last five years. By this time he's earned respect as a world-class player and dedicated servant of the club—the same kind of respect that Lahm and Schweinsteiger were given at the same age.
Mueller's benching in some key matches and often not being used for the full 90 minutes are legitimate causes for concern, but his playing in a variety of positions should not be misinterpreted as him being simply shuffled around as though he were a junior player.
Unlike many who are decisively more skilled in certain positions than others in which they are often used, Mueller actually is near-equally potent no matter where he is played. Mueller scored eight goals in 15 games in which he was used behind a main striker, four in 10 in which he was used as the center forward, 11 in 21 in which he lined up on the right wing and two in four in which he played on the left. All of these rates stand at or within a goal of 0.5 goals per game.
The curious part of Mueller's versatility is that he does not at first glance give the impression of a player who can operate anywhere. His right foot is much better than his left, yet he manages to consistently score even when he's on either wing. His heading as well is good but unremarkable. And yet, when used in a central role as either a support man or an out-and-out center forward, he regularly hits the target and often does so with his head.
Neither his skill with his weak foot nor his aerial ability is suggestive of a top finisher, yet Mueller manages to find the net at near-equal rate from any attacking position. It is, however, relevant to note that Mueller's playmaking ability is much better from a central position behind a main striker than anywhere else. Wherever used, though, he's always good for a goal or at least some scoring chances. And that is what makes him such a devastating attacking player: Opponents can't prepare to face the all-rounder, especially if he doesn't entirely understand his own role.
Although his previous worries were certainly legitimate, Mueller being used in four positions is not actually due to him being just a "fill-in" player. It actually is a testament to his consistency and adaptability that is unparalleled among attacking players in today's game. He just may not have known it until recently.