Fabio could replace suspended and fined brother Rafael

The pair create regular confusion at Old Trafford, often deliberate, and have even bemused match officials during their time in England.

At Barnsley last season, referee Chris Foy booked Fabio instead of Rafael, so it is easy to see how Ferguson might get away with fielding one instead of the other.

"I could play Rafa and say he was Fabio quite easily. There is no way they could know," he laughed.

"Probably they have the same DNA. Maybe it wasn't Rafael who was sent off last week? It is definitely a thought.

"The referee booked the wrong one at Barnsley, so one day you could play one in the first half and the other in the second."

Ferguson's joviality betrayed a tough decision for the United manager, with Fabio, John O'Shea and Wes Brown all in contention to face Birmingham at the start of a crucial four-day period that includes a trip to Blackpool, which Rafael will return for after being handed merely an 8,000 fine and a warning for his remonstrations to Mike Dean at White Hart Lane.

Back-to-back victories would leave the Red Devils in pole position to regain their title, registering a record 19th championship in the process.

Not that Ferguson can afford to take anything for granted against a team that snatched two points off United thanks to Lee Bowyer's last-gasp equaliser at St Andrew's on December 28 and for whom the phrase "hard to beat" could have been invented.

"We are expecting the same battling virtues from Birmingham that we saw at St Andrew's," said Ferguson. "They do have fighting qualities in their team. They will play five across the middle of the pitch, will keep possession and try to make it difficult for us. But at Manchester United, when you play against teams who have a certain way of playing, you have to find solutions."

One answer could be the return of Paul Scholes, who has missed 10 games with a groin injury but was denied an introduction from the substitutes' bench at Tottenham last week when Rafael was given his marching orders.

With Park Ji-sung still absent due to South Korea's ongoing presence at the Asian Cup, Ryan Giggs may make his 601st league appearance, knowing there are plenty more in the pipeline now a new one-year contract has been agreed in principle.

The Blues have made nine visits since Frank Worthington scored their last goal at the stadium in 1981.

Birmingham manager Alex McLeish believes Manchester United can emulate Arsenal and go through the season unbeaten in the Barclays Premier League.

McLeish said: "I think it's ominous, the fact that they've got to this stage unbeaten and their form is probably gathering momentum.

"It's amazing that they are unbeaten and I think that they can only get better."