Brentford striker Donaldson pinching himself over Chelsea chance
And, after stints at Harrogate, Scarborough, Halifax and York, he says walking out tomorrow in the fourth-round replay will be a new career high.
He added: "It's the biggest game of my career. From where I started off - grotty pitches at Harrogate Town - to Stamford Bridge.
"It's unbelievable - to get the opportunity to play at their stadium and try and knock the European Champions out of the FA Cup.
"The worst of my career was Barrow away. It was raining and we lost. From there to Stamford Bridge doesn't really compare."