The seasons of Michael Carrick and Darren Fletcher offer disparate tales of two Manchester United midfielders. As Sir Alex Ferguson hails the "best ever" campaign for Carrick, the manager sees Fletcher's season is now over due to surgery on the ulcerative colitis that also forced him to miss last term from late November.

Then, Fletcher managed 10 appearances in United colours, the same number he recorded until a late substitute appearance in the 4-3 Boxing Day win over Newcastle United proved this season's final act. Of the operation, Ferguson says: "It was something we thought would happen. We tried to manage the condition with the treatments he was using. But in the last couple of weeks the problems came back. We hope this operation can solve the problems he has in terms of his career and expect him back in July. It's a blow for the boy but given he's been dealing with the condition for a couple of years now, this is just another step in terms of his health and his career."

What United miss is the pre-illness Fletcher, whose drive propelled midfield and who had a welcome habit of scoring when it mattered. One illustration is the defining goal of Fletcher's career. This came seven years ago when a looping header at Old Trafford gave United a 1-0 win over Chelsea and ended the London club's 40-match unbeaten run.

It came at the close of the week in which Roy Keane had left the club after an X-rated interview to MUTV that was never aired and that featured a tirade aimed at the quality of some United players, one of whom was Fletcher. The Scot was then 21 and had just announced himself. Now, he faces a pre-season slog through next summer before trying to re-establish himself as a first-team regular.

"Attitude is not in question," Ferguson says. "There will be no problem with that. He's a fantastic character, a brilliant boy and he will do his very best. He will need time to recover from the operation and that will be quite a while. This [the operation] will improve his prospects. He has had to change his game. When he played the games he did this season he wasn't the Darren Fletcher we knew. He was sitting in front of the back four and did that very well. When he comes back – and I'm sure he will – it will be in a different role."

This is the position where Carrick now flourishes and his ascent to become one of the brightest stars of the United constellation makes Fletcher's ill fortune sadder. Since Carrick's transfer in summer 2006 from Tottenham Hotspur, to where United travel for Sunday's late game, he has gradually eased into the role of midfield conductor.

"He has been absolutely magnificent," Ferguson says. "It is his best-ever season at the club. He is completely in command of that position now. Even when he came on Wednesday night [in the 1-0 FA Cup win over West Ham United], he just settled it, got a grip of the game immediately – good players do that. He got a grip of it and eased us through that last 20 minutes."

As Paul Scholes has grown older Carrick has taken over to return increasingly better numbers. Of United's 22 league games so far he has started in 21 – nobody has played more – and already there have been 1,716 passes with an accuracy of 88.23%. Last term, his best until then, Carrick made 27 starts and 2,192 passes of which 90.1% were on target. If he stays injury free he should dwarf these figures.

Yet for some he continues to be the Marmite in United's midfield. He is either the slide-rule pass master who sees clearest in the heaviest of traffic – or the man with two more gears but content to coast along in third.

In the latter camp may be counted a host of England managers who since his debut 12 years ago have awarded him only 26 caps. Sven-Goran Eriksson, Steve McClaren, Fabio Capello and Roy Hodgson have all taken a look and decided Carrick could not be England's central linchpin, facing competition from Steven Gerrard and Frank Lampard among others.

A prevailing criticism is a lack of goals and consistent marquee performances. Carrick has no league strikes this term, scored only two last season and his career best is the four managed in the 2008-9 campaign.

"I've always found Michael Carrick can split fans' opinion," says Barney Chilton, editor of the club's oldest fanzine, Red News. "On the one hand there are those who thrust his stats and pass completions at you like the Bible. On the other, the non-believers who only give grudging respect during consistent periods. The reality is he's a ball player, which pleases the former, but because he's not also a world class ball winner – or tough tackler – this irritates the latter.

"It was no coincidence that United's resurgence after 2005-06 [when they had not won the title for three seasons] came with his arrival. His peak before this season was on the road to Moscow [and the Champions League penalty shootout win over Chelsea in 2008]. He uncomplicates the game. Perhaps because he's the quiet, unassuming man, fans want him, still, to grab games by the scruff of the neck, when it's not his manner, though a pass like Newcastle at home can decide a game [for the winner on Boxing Day]. He's one of those Marmite players."

Ferguson will hope that next season he and a resurgent Fletcher can finally fulfil the potential their partnership offers.