The biggest threat to their promotion ambitions this season is surely their mounting injury list, which has seen the entire right side of their defence decimated and a number of strikers ruled out for varying lengths of time.
United looked at free agent Andre Wisdom but decided against signing him, although Heckingbottom admits United are “serious” about bringing a free agent in.
So we scoured the free agent market to pick out 12 players who could possibly do a job for United – click through our photo gallery to have a look ...
1. Winston Reid
Formerly of West Ham, the New Zealand international was most recently on loan at Brentford, playing in last season’s play-off final to help the Bees into the Premier League. Getting on at 33 but could be good cover for John Egan and help Kacper Lopata and Co. develop Photo: Catherine Ivill
2. Hal Robson-Kanu
Another potential option in attack, Robson-Kanu would offer a physical presence for the run-in after leaving West Brom recently. Can also play wide Photo: Pool
3. Marc Navarro
A player with experience, albeit briefly, of playing in England from a spell at Watford which came to an end last summer. Mainly a right-back, he can also play in the centre – which could be ideal considering United’s troubles in that area Photo: Richard Heathcote
4. Jerome Sinclair
Out of contract after leaving Watford at the end of last season, Sinclair has hardly set the world alight since leaving Liverpool as a youngster but clearly has some ability to have played for the Reds and England’s youth teams. If Billy Sharp is out for any time, he may provide something different Photo: Dan Istitene