Not good.

Three-time European champions Leinster made light work of Premiership leaders Northampton Saints yesterday afternoon in the Champions Cup, smashing the English side 43-16 in Franklin’s Gardens.

But the win may have come at a huge cost with Ireland international Johnny Sexton going off early on in the second-half with what looks to have been a very serious knee injury.

Sexton looked to be in some pain after twisting his knee very awkwardly. After the game head coach Leo Cullen said the full extent of the problem won’t be known until Sexton gets a scan.

“He has a bit of strapping on his knee,” said Leo Cullen after the game.

“He will get a scan tomorrow (or Monday) and we’ll see what sort of extent it is. He’s a little uncomfortable there at the moment”

“I don’t know the extent of it, but we’ll find out the extent of it. We’ll find out more (in the) early part of next week.”

Check out footage of the incident below. It does not look good at all.