The only references I have found are two tweets from @citypolice yesterday:
"Woman cyclist suffers serious head injuries after a collision with a tipper truck in the City this morning. (1/2)"
"If you witnessed the incident at 7.55am at St Botolph Street - Houndsditch junction please call 101 & ask for City of London Police. (2/2)"
Access to Leadenhall Street from Gracechurch Street was still closed around noon yesterday.
Best wishes to the rider.