The huge amount of injury time was due to Leeds' highly-rated 18-year-old Clarke being taken ill -- with the game being stopped for seven minutes. He received medical attention before he was stretchered off while being given oxygen and then taken to hospital.

"What we know is that he didn't feel well," Leeds manager Marcelo Bielsa said.

"We don't know the reasons yet. But when he was taken to the dressing room he was better. He was taken to hospital to see if he is alright."

Leeds later issued a statement reassuring fans about Clarke, who had been taken off at half-time.

"The player is responsive and attending hospital with the club's head of medicine and performance.

"On behalf of everyone at Leeds United, we would like to thank the medical staff from both clubs for their response to the incident."

The draw sends Bielsa's side a point clear of Norwich at the top though the Canaries can reclaim that position if they beat East Anglian rivals bottom-placed Ipswich Town on Sunday.

Sheffield United lie in third position -- three points off Leeds -- after missing a golden opportunity of going top themselves, surrendering a 3-0 lead on Friday to be held 3-3 by Aston Villa.

'Formidable partnership'

Boro had taken the lead through Lewis Wing two minutes into the second half, slotting home from George Friend's cut-back.

Leeds -- who have had a poor run of late losing four of their last six matches coming into Saturday's game -- should have levelled in the 71st minute.

Patrick Bamford returning to his former club -- for whom he scored a hat-trick against Leeds last year -- fired wide from four yards out with the goal gaping.

Middlesbrough's Ireland goalkeeper Darren Randolph also kept the hosts' noses in front with some stunning saves, thwarting Kemar Roofe twice.

Bielsa felt his side should have come away with all three points.

"If we take into account the 15 minutes in the first half when we were not at ease, apart from this we dominated the game," said the former Argentina and Chile national coach.

While Leeds have faltered since the turn of the year the form side has been Bristol City who made it eight successive wins in all competitions, eking out a gritty 1-0 away win over Blackburn Rovers.

Lee Johnson's team -- who he guided to the League Cup semi-finals last year -- are still 11 points off Leeds but have two games in hand on the table toppers.

Johnson credited his centre-backs Adam Webster and Tomas Kalas for securing the points.

"They're top centre-backs, those two (Webster and Kalas)," said Johnson.

"We went as big as we could go to get Webster and he's got better and better.

"And Kalas is well proven and enjoying his football.

"They are a formidable partnership."