The testimonial has been pencilled in for August. For Paul Scholes, the search is now on for suitable opponents and "a good, proper game". Real Madrid would be popular with the fans, so Cristiano Ronaldo could play once again at Old Trafford. Or Barcelona maybe, the side he loves to watch and that, in many ways, symbolise his own brand of pass-them-to-death football – quick, elusive and, when everything clicks, bloody brilliant.

He is talking in a quiet side room at Manchester United's training ground. Scholes, as usual, has been one of the first to arrive for work, his hair still damp from his morning shower. Training top, jeans, the same haircut he has had since he was playing for Boundary Park Juniors almost 25 years ago. Scholes has never been one for designer labels or flashy cars, and it is almost a surprise to find out he has accepted the offer of a benefit match. Already, you can imagine the adulation from the stands and the polite, unassuming little wave from a man not really comfortable with all the flashing bulbs.

But wait. When a footballer starts talking about his testimonial it usually means only one thing. At 36, Scholes is now at the age in football when the legs can betray the mind. Ryan Giggs, a year older, has already signed a one-year extension but Scholes has a longer history of injury issues. It is a serious possibility this weekend could be his last Manchester derby and the next few weeks could represent the countdown of his United career.

At the very least, he is clearly contemplating the end-of-season press release. "I'll decide at the end of the season," he says. "I really don't know what I am going to do yet. I've got these games to think about now and I will decide from there. People always say you should play as long as you can but there comes a time when you can't physically do it. I'm wary of that. I just want to make sure it is done at the right time."

Football would be losing one of its greats. Scholes would need a small warehouse to show off all the trophies he has won since his debut in a League Cup tie at Port Vale 17 years ago. It is hard to believe that a footballer-of-the-year trophy is not among them; even harder that a local MP threatened United with the Trades Description Act for playing a young Scholes, David Beckham and Gary Neville that night at Vale Park.

The list of those who have since described Scholes as the best footballer in England includes, among others, Zinedine Zidane, Thierry Henry, Marcello Lippi and Edgar Davids. Or ask about Scholes at Manchester City. Only three other United players – Sir Bobby Charlton, Eric Cantona and Joe Spence – have bettered Scholes's tally of seven goals against the old enemy. The last was a stoppage-time winner at Eastlands last season. "It was perfect," Scholes remembers. "That was a major highlight of my career, one of the best things I have ever done." He has struggled, by his own admission, to cope with being on the edges of the team this season (not starting either of the Champions League ties against Chelsea). "It is very difficult to accept [not playing every game] but the time comes when you know that you can't. You want to think like a 25-year-old, you like to think that you can play every game. But you can't. You just have to make sure you are ready for the odd 20 minutes here and there. It's hard to make that adjustment. It is not nice."

This was in his thoughts when he turned down the chance to play in last summer's World Cup. Scholes did not want to risk it affecting his club form, although, looking back, he does not think fatigue would have been an issue.

"They played only four games! I think it is more a mental thing. You're away a long time. And the players who went to South Africa will feel it [mentally] because it wasn't great, was it? They didn't play very well. They took a lot of stick. And things like that take a while to get over."

But he does not want to dwell on the subject much longer. There is, after all, the small matter of an FA Cup semi-final against Manchester City on Saturday and, as one of the few Mancunians involved, Scholes is better placed than most to comprehend why a United defeat would mean "we probably won't ever hear the end of it". Scholes has been playing long enough to remember when City were grubbing around for points in the Second Division, what is now League One. Then and now seem a long time apart. "It's an FA Cup semi-final at Wembley, it's massive, there will be 30,000 fans from each side... it's the biggest game we've had against City for a while. Whoever loses will be devastated."

He knows this from experience. "I remember the 5-1 in 1989 and Andy Hinchcliffe scoring that goal [Hinchcliffe celebrated by holding up five fingers to United's fans]. It's painful. I can also remember going to Maine Road and losing 3-1 [in 2002] and it's horrible. You hate losing against anybody, but City? It's bad."

These are the words of a man brought up to believe that Manchester's other club always have to be put in their place. "We have always been the team that has done better, right back from when I was a kid," he says. Later, Scholes talks of an attitude at Old Trafford in the 1990s that there was "no way" they could lose to their neighbours.

There is a smile, too, as he considers that City have beaten United only once in eight attempts since Abu Dhabi's royal family made them the most financially endowed football club on the planet. "They will be pissed off about that. Even then, that game was a [Carling Cup semi‑final] first leg, with us having another game to make up for it. We have made a habit of nicking games in the last minute. I've done it, Michael Owen's done it, Wayne [Rooney] did it last season and, again, with his unbelievable goal in the league this season. That's the difference between the two teams. We have a belief that we can beat anybody, but if City have that, I'm not too sure."

Conversely, he believes the huge amounts of money being pumped into City have "probably helped us a bit. It has spurred us on when we have played them. It has made us concentrate a little bit more than we normally would against them."

City, he knows, are desperately craving a trophy. "When they are fourth or fifth, or wherever they are in the league, I don't think they can be classed as a main rival. Our main rivals are obviously Arsenal and Chelsea. I think City are just a rival because of where they are [geographically], and Liverpool the same." It is a sentence delivered with every bit as much snap as one of his famous late tackles.

Sir Alex Ferguson almost always plays Scholes in these fixtures, eager to involve a man who understands the importance of local rivalries. But Scholes is not taking it for granted. "I thought the team looked brilliant in both games against Chelsea. I never felt we were in any danger of not going through." He praises Michael Carrick, the man who has taken his place, for "coming back into form – he's been brilliant the last few weeks".

Tuesday night was also the first time Scholes started to think this team could emulate the 1999 treble winners. "Until we beat Chelsea I don't think it had crossed any of our minds. It might have crossed other people's. But there were too many games, it seemed too far away and we had a big team like Chelsea in front of us in the Champions League. But we're in the semi-finals in Europe now, the semi-final of the FA Cup and we're seven points clear in the league."

And, though he does not say it, you wonder whether Scholes has pondered if a European Cup final at Wembley could be a great way to bow out. They will hope not, at Old Trafford and way beyond. But not at City.