Saturday is the birthday of Harry Redknapp and Mauricio Pochettino and the managers will mark the occasion by fighting over the same present. Three points constitute the ideal gift for both men but with Queen's Park Rangers travelling to Southampton, only one will be able to celebrate on the first occasion opposing managers in the Premier League have shared the same birthday.

For Pochettino a draw might just be tolerable but for Redknapp, who is exactly 25 years older than his counterpart and, more pertinently, seven points from safety with only 11 matches left to clamber out of the relegation zone, sharing is unacceptable. Southampton remain in trouble, too, but that is not the only reason their supporters will not be wishing Redknapp a happy return.

This will be the first time Redknapp has gone back to St Mary's since a grim year in charge in 2004-05, when he was parachuted in to lift the club higher than 18th place and proved unable to stop them falling to the bottom of the table, ending a 27-season stay in the top flight. Redknapp remained in charge for a few months in the Championship before accepting an offer to defect back to Southampton's arch-rivals, Portsmouth, whom he did guide to survival. For the Saints faithful he is the ultimate sinner.

"I will get a bit of grief, won't I?" he says ahead of Saturday's return. "No one was more upset than I was that the club got relegated that year. I gave everything I had and that's all you can do. No one tried harder than I did … I stayed there in the Championship the following year and gave Theo Walcott his debut and then I got a phone call asking me to go back to Portsmouth, who looked like they were going to get relegated.

"You make decisions and you get on with it. I don't regret it, I had a great time at Portsmouth again. I took a gamble because if Portsmouth had got relegated that year I would have been finished. But I managed to keep them up somehow."

Redknapp says the reason he was unable to rescue Southampton was that, unlike the Portsmouth and Tottenham Hotspur teams he subsequently hauled to safety, their players were not good enough. "When I have been successful and done well at Tottenham, it is about good players," he explains. "That is what the game is about. If you've got good players, it is an easy game. You send them on the pitch and off they go. They perform week in, week out. It's easy and the better players you've got the easier the job is."

The question now, then, is whether he has got good enough players at QPR. They looked substandard under Redknapp's predecessor, Mark Hughes, going without a win in the first 12 Premier League matches of the season, the last of them being November's 3-1 home defeat by Southampton, which led to Hughes's dismissal and Redknapp's recruitment.

Upon his arrival Redknapp declared that he had the raw materials to forge a decent unit and, true enough, he did oversee improvement. His first step was to solidify a crumbly defence and QPR drew their next three matches before claiming their first win of the campaign with a 2-1 win over Fulham, when Adel Taarabt scored both goals and generally sparkled, vindicating Redknapp's decision to make him the focal point of the team rather than stationing him out wide as Hughes had done.

The side looked more balanced and better drilled than under Hughes. They lost their next three matches but then summoned a staggering 1-0 win at Stamford Bridge and took six points from their next four games. It seemed they had momentum – but they could not sustain that and the limitations of the new approach were exposed. Sitting deep, ceding possession and defending in numbers made QPR more difficult to penetrate but even less likely to score.

Under Hughes they scored an average of 0.75 goals per game, under Redknapp the rate has dropped to 0.64, hardly surprising when they have had less of the ball and made fewer passes and crosses. Alarmingly, the freshness that followed Redknapp's appointment has seemed to fade in the last two matches, with rotten displays bringing defeats by Swansea City and Manchester United. The momentum looks downward again.

In fairness, Redknapp foresaw this and his plan to move to a second phase of revamping has been hampered by injury to Loïc Rémy, the striker signed in January to spearhead an attacking approach on the newly solid platform. The Frenchman scored on his debut in a draw at West Ham but was injured in his third game. He is fit to return against Southampton but now Bobby Zamora has damaged his ankle, meaning Redknapp still cannot field the strike duo he describes as his "dream".

Southampton's defence has been their weak spot this season but QPR look ill-equipped to exploit it; meanwhile, with Christopher Samba yet to justify his expensive January transfer, QPR's capacity to keep the attack-minded home side at bay is questionable. Southampton are three points above the relegation zone but Redknapp reckons they are too good to go down. Similarly, although this is their first season back in the Premier League since their demotion under him, he says he always knew they had the wherewithal to recover.

"OK, they had to take a couple of steps backwards, they went down to League One, but you knew when you looked at it that they were going to come back. They've always had a good infrastructure … great stadium, fantastic training ground, great youth setup producing kids like a conveyer belt, they've always done it. They were never a club that was to disappear with no foundation."

Asked whether QPR are equally equipped to recover if they are relegated, Redknapp's reticence is telling. "It's different," he says. "I'm not going to say something that's going to cause a problem for me, I don't need that. It's different."