Four Man Utd hotheads are in danger of missing Barcelona second leg if they are booked at Old Trafford
The Red Devils host Barca at Old Trafford tomorrow night before the return leg at the Nou Camp next Tuesday
NO fewer than FOUR Manchester United players will need to be on their best behaviour tomorrow night - because a booking will rule them out of the second leg.
Ander Herrera, Luke Shaw, Nemanja Matic and Ashley Young are all one yellow card away from a suspension.
Right-back Antonio Valencia is also one short of a ban but is expected to be ruled out of the game so is not at risk.
Nelson Semedo, meanwhile, is the only Barcelona player who could miss the second leg for his accumulation of yellow cards.
Uefa regulations state that "from the first match in the group stage, a player is suspended for the next competition match after three cautions in three different matches".
So with the five Red Devils all picking up two cautions in the competition already, they will go into the clash at Old Trafford desperate to keep in the referee's good books, rather than his note book.
Shaw may well have the toughest task trying to avoid a yellow card as he will have to deal with Lionel Messi drifting out to the right and causing the English left-back problems.
On the other side, it is unclear who will start at right-back for Ole Gunnar Solskjaer's side with Young and Diogo Dalot both viable options.
Young is likely to get the nod - due to his experience and form - but if he mistimes a tackle or shows some dissent, he could well miss the trip to the Nou Camp next Tuesday night.
In midfield, Herrera and Matic remain doubts for United and did not train with the first team today.
Herrera - who has only played twice in the Champions League so far this season - missed the defeat at Wolves last week with a knock and might not be fully fit and ready to play, let alone start.
Scott McTominay scored his first United goal in the Molineux loss.
And with Paul Pogba back after missing the second leg against Paris Saint-Germain through suspension, Matic may well miss out on a spot in the Manchester United starting XI.
There is more good news for Herrera, Shaw, Matic and Young if they can get through tomorrow's match without a booking.
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Uefa's decision in 2014 to change the ruling on yellow cards being 'wiped' after the quarter-finals means suspensions for the final are now rare.
Famously, Roy Keane, Paul Scholes, Xabi Alonso and Branislav Ivanovic all missed Champions League finals because they picked up a third yellow card in the semi-finals.
But it would now take a red card in the semi-final second leg to suspend a player for the final.
