IF Gavin Johnson was once a model of uncertainty, he is no longer quite so sure of himself. Saracens' imposing South African full-back agonised long and hard before throwing in his lot with the north Londoners and spent much of this season doubting whether his rebellious body would allow him to play more than a walk-on part in his club's courageous challenge for a first professional league and cup double. Now that he is playing, he is in two minds as to whether he should continue doing so. Truly, his indecision is final.

Under the circumstances, it is a minor miracle that he should have pulled off the most decisive tackle of the season to date; an inspirational flash of defensive brilliance that may yet win Saracens the Allied Dunbar Premiership. "Yes, that was an important tackle," he says, recalling the last minute - nay, last second - corner-flagging hit that denied Jamie Williams, his Harlequins opposite number, what would have been a match-winning and Premiership- deciding try at The Stoop 10 days ago. "I'm quite proud of that one.''

It is perfectly conceivable, likely even, that Johnson has only two games of big-time rugby left to him. A lifelong fisherman and passionate wildlife enthusiast, he has a 40-kilometre stretch of virgin Zambian game reserve waiting for him the moment he retires and he is currently weighing the obvious attractions of a Hemingwayesque life in the Upper Zambezi against the prospect of another season of tough Premiership activity in lower Watford. Well, what would you do?

Less than a month ago, Johnson's mind was uncharacteristically close to being made up; after Saracens' outstanding semi-final victory at Northampton, the guarded and very private Springbok from the Transvaal quietly let it be known that he would leave England at the end of the season and take over the management of his Zambian business interests in person. At which point, the Sarries management asked him to reconsider. He has been chewing the fat ever since.

"It's 95 per cent certain that I'll go back to Africa," he said this week. "The game reserve is upstream of Victoria Falls; remote, untouched and extremely beautiful. We have hippo and crocodile, outstanding fishing and wonderful bird life. It's a dream, really. I've always had a serious love affair with the bush, with wild Africa, and the chance to combine that passion with a business venture of huge potential excites me.

"Having said that, the reserve is in dependable hands at the moment and there is no good business reason why it shouldn't stay that way for another season. I have another year on my Saracens contract and while they're happy to release me if I decide to go, they've asked me to consider staying on. Six months ago, I wouldn't have given it a second thought. Now, though, I'm enjoying my rugby so much that it's a possibility.''

Johnson was born into South African farming stock 31 years ago, played three Currie Cup finals with Transvaal and emerged as a serious Test challenger to Andre Joubert, the Rolls-Royce of Springbok full-backs. He made three appearances in Francois Pienaar's triumphant 1995 World Cup-winning campaign; indeed, he confronted Gareth Rees, the Canadian Wasp who opposes him today, in what became known as the Battle of Boet Erasmus. Neither went the distance; Johnson withdrew with concussion while Rees was sent off for trying to concuss everyone else.

It was Pienaar, now Saracens' player-coach, who first planted the seeds of an English sojourn in Johnson's mind. "He was looking for a full-back and thought of me. I gave him an adamant 'no way' at first but he talked me round. I'd signed a three-year contract with the South African union, but Louis Luyt obliged by releasing me early and the next thing I knew, I was here in London.

"I'd been in the British Isles before - I played for Blackrock College in Ireland for six months - but I don't suppose for a moment that I'd have come back had it not been Francois' idea. His leadership of the Springboks was quite outstanding and if anything, his abilities are even greater now. He always makes you feel that victory if possible, that you can achieve the ultimate on a rugby field, and his impact here at Saracens has been something else.''

Frustratingly, any early impact Johnson might have made was blunted by injury. Saracens knew he was a high-quality marksman and an extraordinarily accomplished kicker out of hand - the best in the Premiership, perhaps - but try as their physios might, they could not get him on to the pitch. Even now, he has played only 11 Premiership games for the title challengers and two of those were at the fag end of last season.

"There were two separate problems with my hamstring and my left knee went as well," he said. "I couldn't seem to get myself fit and I ended up feeling pretty negative about things. I came to the conclusion that I'd had enough of rugby and should start thinking about my future outside the game. But the club were very supportive and full of encouragement and in recent weeks, my body has started to behave and I've loved every minute of it.

"Whatever I decide to do - and I'll be speaking to the club next week - I feel very privileged to be playing in an English cup final. I've been fortunate enough to have experienced my fair share of special occasions; Currie Cup finals in South Africa generate fantastic interest and even though I played only seven Tests, one was against New Zealand and another against Western Samoa in a very emotional World Cup quarter-final. Twickenham has a tradition of its own, though, and I'm honoured to be involved in this match.''

Saracens freely admit that Johnson will be difficult to replace, especially now that they have abandoned any thought of shelling out mega-bucks for Tim Stimpson, the disaffected Test Lion from Newcastle. "It's up to Gavin, but he knows how highly we rate him," said Mark Evans, the director of rugby, this week. "You've seen something approaching the best of him in recent weeks and when he plays at that level, he's the Real McCoy.''

Evans can rest assured that for today, at least, his prize full-back is more concerned with the big game at Twickenham than the big game back home. After that, who knows? Certainly not Johnson.