The Rangers striker has proved a revelation since Steven Gerrard brought him to Ibrox last season.
Defoe scored 163 goals in 496 English top flight appearances before joining Rangers on an 18-month loan in January.
And he has continued to bang them in for Rangers, where his record - 21 in 38 - is greater than one in two.
In contrast, Sheffield United are the Premier League's seventh-lowest scorers, despite being sixth in the standings - with a quarter of their overall tally arriving in Saturday's 3-0 win against Burnley.
And Collymore, the former Liverpool and England striker, wrote in his column for The Daily Mirror on Tuesday (page 51): "Sheffield United were one of my tips for relegation and, of course, that might still happen.
"But their football and belief so far, and Chris Wilder’s no-nonsense style of management, have been a pleasure to watch.
"Defensively, they are conceding 0.75 goals a game — Champions League percentages — and what they need now is to push on from a very solid start. To do that they need more goals and if they get them they will be safe.
"I’d imagine a loan striker will be top of Wilder’s Christmas wish-list because if they can get a poacher of Jermain Defoe’s calibre — all relegation bets will be off."
Defoe was a target for Sheffield United prior to his move to Rangers, according to The Star.
But the chances of the 37-year-old being prised away from Rangers mid-season look slim - should Sheffield United again be keen.
And anyway, the Blades' squad already possesses a poacher in the shape of Billy Sharp.
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