Alan Pardew: "We don't think it's too serious, but he is certainly not going to be involved tomorrow."
Newcastle have made something of a habit in recent weeks of winning games at the death with Papiss Cisse contributing late decisive strikes against Stoke, Anzhi and at the weekend, Fulham.
Cisse said: "I tell myself as long as the referee hasn't blown his whistle, the game isn't over.
"I'm an attacker, that's my job - that's what I always tell myself. I have to be ready to score at any moment, so there's always a chance until the whistle goes that I can score."
Pardew will take another winner from the Senegal international whenever it arrives, but admits he has been urging his leading scorer not to leave it so late.
He said with a smile: "I keep telling Papiss to try to score before the 92nd minute - it's becoming ridiculous.
"He's a special goalscorer and a big threat to Benfica, I thought, in the first leg, and he will be tomorrow too."
APRIL PREMIERSHIP FIXTURES
Saturday 13 April 2013 15:00 Arsenal v Norwich Emirates Stadium 15:00 Aston Villa v Fulham Villa Park 15:00 Everton v QPR Goodison Park 15:00 Reading v Liverpool Madejski Stadium 15:00 Southampton v West Ham St. Mary's Stadium
Sunday 14 April 2013 12:00 Newcastle v Sunderland St James' Park 14:05 Stoke v Man Utd Britannia Stadium
Tuesday 16 April 2013 19:45 Arsenal v Everton Emirates Stadium
Wednesday 17 April 2013 19:45 Man City v Wigan Etihad Stadium 19:45 West Ham v Man Utd Boleyn Ground Saturday 20 April 2013 15:00 Fulham v Arsenal Craven Cottage 15:00 Norwich v Reading Carrow Road 15:00 QPR v Stoke Loftus Road Stadium 15:00 Sunderland v Everton Stadium of Light 15:00 Swansea v Southampton Liberty Stadium 15:00 West Brom v Newcastle The Hawthorns 15:00 West Ham v Wigan Boleyn Ground
Sunday 21 April 2013 13:30 Tottenham v Man City White Hart Lane 16:00 Liverpool v Chelsea Anfield
Monday 22 April 2013 20:00 Man Utd v Aston Villa Old Trafford
Saturday 27 April 2013 12:45 Man City v West Ham Etihad Stadium 15:00 Chelsea v Swansea Stamford Bridge 15:00 Everton v Fulham Goodison Park 15:00 Southampton v West Brom St. Mary's Stadium 15:00 Stoke v Norwich Britannia Stadium 15:00 Wigan v Tottenham The DW Stadium 17:30 Newcastle v Liverpool St James' Park
Sunday 28 April 2013 13:30 Reading v QPR Madejski Stadium 16:00 Arsenal v Man Utd Emirates Stadium
Monday 29 April 2013 20:00 Aston Villa v Sunderland Villa Park
Source: Newcastle United Mad