Chelsea manager Mauricio Pochettino fumed his Chelsea side were not 'mature enough' after seeing his side twice surrender the lead to draw 2-2 against bottom side Sheffield United.
Thiago Silva and Noni Madueke scored either side of the break to put Chelsea 2-1 up, with Jayden Bogle scoring for the Blades just after the half-hour mark.
Just when it looked as though Chelsea were on course to claim all three points, McBurnie struck in the third minute of stoppage time.
'At 52, you identify really quickly whether the team is ready to compete or not. Maybe this group is not mature enough to compete in games every three days. It's a new team and we are still learning about their profiles.
'The process always takes time. It's not a magic thing. It's a project, a three or five year process to build a team.
'We are in the semi-finals of the FA Cup. We were not in a good position in the beginning, but that's normal. We need to accept it now and work to try and fix our problems,' he added.
The Argentine is under pressure to get results and show an improvement in performances during the end-of-season run-in after being backed heavily in the transfer market.
He has outlasted his predecessor Graham Potter who was sacked after less than seven months in charge and the first manager to fall victim to Todd Boehly's reign.
Pochettino said: 'It is very frustrating because when you concede in the last few minutes you feel very disappointed and frustrated because you should win the game.
'We had the possession but didn't create enough. I think in the first part of the season we were a little bit more solid. We were creating but we weren't clinical. Now we are scoring more but we are conceding more.
'The difficult thing is to find the balance. The
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