The Evening Standard reported that David Wade, 52, had to shout for help after the robbery - which took place at 8.20pm on July 2.
He also had set off a fire alarm before he was rescued by a passer-by.
The two robbers took Wade’s wallet and phone before swiping £300 in tennis court fees from the safe in Waterlow Park, Highgate.
The gardener has now launched a personal appeal for witnesses to come forward as a police investigation continues.
He said: "I just want to get these people before they do it to someone else. If they did that for a few hundred pounds I hate to think what they might do to someone else."
A Met Police representative told the London newspaper that two men, aged 34 and 23, had been arrested on suspicion of aggravated burglary in connection with the attack and bailed until September.
A Camden Council representative said the council was working with the police over the incident.