Abdul Omer Mohsin, the sacked trade union convenor and bus worker, is back in hospital after being taken ill on Sunday.
He had previously signed himself out of hospital to attend his employment tribunal, which took place in Watford last week.
The tribunal revolved around disputed accounts of a meeting at Abdul Omer’s workplace.
The judges accepted management’s account of proceedings rather than Abdul Omer’s and upheld his sacking.
Abdul Omer maintains that he was removed from his job in April 2010 because of his trade union activities.
He played a prominent role in a pay campaign at London Sovereign buses.
His legal team, which was provided by the Unite union, are considering whether there are any grounds on which to appeal the verdict.
Abdul Omer’s workmates have refused to elect another convenor and have made his case part of their wider pay campaign.
Drivers at both Edgware and Harrow garages have voted to ballot for strikes over his sacking.
It is difficult for workers to win at employment tribunals.
Of 47,900 unfair dismissal claims between April 2010 to March 2011, 4,200 won at a tribunal. In only eight of these cases did the tribunal order reinstatement.