When Rafael left Craven Cottage in a protective boot on Saturday, it started a scramble for Manchester United's right-back spot.
David Moyes has plenty of options. Chris Smalling and Phil Jones can play there and have done for England as well as United in the past. Antonio Valencia has also been used as an emergency full-back both this season and last.
But none of the them are full-backs by trade. Smalling and Jones prefer to play in the centre of defence, and Valencia is a wide midfielder.
If only there was a clone of Rafael to take over when he's injured. Oh, that's right, there is.
But while one Brazilian twin was left in Manchester nursing strained ankle ligaments that could keep him out of Arsenal's visit to Old Trafford on Sunday, the other, Fabio, couldn't even get in the 18-man squad for Tuesday night's draw against Real Sociedad.
It spells danger for a player whose contract is set to expire next summer.
Fabio has appeared just twice under Moyes.
He didn't do much wrong at right-back when Crystal Palace were beaten 2-0 at Old Trafford in September. But three days later, against Bayer Leverkusen in the Champions League, he was back on the bench, replaced by Smalling.
On as a substitute against Norwich City in the Capital One Cup, he scored United's fourth from midfield. But he was soon back in the stands watching the win over Fulham.
There is little doubt that Rafael has developed a lot quicker than his brother. Fabio still looks like the 2010 version of the Da Silva twins, the version that dives into rash challenges and switches off every now and again.
But Rafael was one of the best right-backs in the Premier League last season. And there's no reason why Fabio can't follow that same path, even if he is just a little bit behind schedule.
Fabio arrived at Old Trafford from Fluminense in 2008 with the more established reputation after starring for Brazil at the 2007 Under-17 World Cup. But his chequered injury record, and a loan spell at QPR last season, means he's only made 55 appearances in nearly six years at United compared to Rafael's 138.
But experience is the only noticeable difference between them.
Moyes faces a dilemma in the coming months. He can take a leap of faith and trust that Fabio will turn into another Rafael or he can let him walk away in the summer.
The decision will be much easier if Fabio is given a chance to gain the experience that has proven so valuable to his brother. If only United needed a right-back.