Far from being "cavalier or gung-ho", his lawyers insist he put no pressure on his students to go beyond their safe limits.
Frank Burton QC, for Mr Ahmed, said he came to grief "during a descent described variously as a slope, gully, drop off or bombhole at part of the route known as Barry Knows Best".
He was injured when his front wheel suddenly jammed on "what looked like a clumpy, grassy piece of ground", the High Court heard.
He came off his bike head first over the handlebars and impacted on the front of his head, just above the forehead.
And the QC told the court: "A mountain bike rider who is on a course for beginners and is a novice should not be catastrophically injured in the first 75 minutes of an introductory training course.
"A novice rider on a first training course should expect the instructor to pick the terrain, to pick the course, to pick the method of training so the risk is minimised, so this accident should not have occurred.
"The accident occurred because of defective instruction and defective teaching."
Mr Burton added that Mr Ahmed, who still works as a senior lawyer for Philip Ross Solicitors, is "educated and articulate" and "not a thrill seeker".
Before the accident he went to the gym three or four times a week and played cricket on a Sunday.
He had been riding a mountain bike for several years but this was the first time he had any training.
Although experienced in cycling and mountain biking, he was a novice to "rough terrain" and "descents".
The beginners skills course, costing £79, was designed to help riders tackle more "technically demanding terrain in a safe and controlled manner".
Mr Justice Jeremy Baker said the real issue was "whether Mr MacLean sufficiently enabled Mr Ahmed, by training and the like, to complete the slope with safety".
But Mr Burton claimed the instuctor "progressed this group too fast" and had a "minimalist" and "lazy form of teaching".
"The instruction on this occasion was woefully inadequate," he told the judge.
The accident victim believed he had been instructed 'to descend the gully at speed and without braking', the court heard.
But Mr MacLean denies all blame, saying that Mr Ahmed rode down the 'wrong part of the track' and then, on a second attempt, 'made exactly the same error'.
"I am 100 per cent sure he made the same mistake twice," he told the court.
"I was surprised at the time. It has been on my mind for four-and-a-half years and I am absolutely positive it happened."
Tim Horlock QC said Mr MacLean, who is also a teacher, was a "reliable witness and a careful and considerate instructor".
"He is the very opposite from the picture that is sought to be painted of a cavalier or gung-ho, authoritative or rushed, instructor," added the QC.
Mr Ahmed's mountain biking experience 'was significantly greater than one might have been led to believe'.
The instructor did not "rush" the group or "progress them too fast", insisted Mr Horlock.
Mr Ahmed "knew that he could walk when he wanted to' and that 'he was under no pressure to undertake anything which he thought was beyond him".
Mr MacLean had "satisfied himself by the time they got to Barry Knows Best that they were ready for it", added the QC.
And Mr Horlock told the judge that mountain biking involves risk "by its very nature".
"There was nothing unreasonable about permitting Mr Ahmed, a mountain biker of 12 years' experience, to have a run down the slope once, or more than once," he said.
Mr Justice Baker will give his ruling on Mr Ahmed's case at a later date.
