Neal was dispatched to Roots Hall after it was confirmed that Zak Brunt, the United midfielder, would join Notts County for the second half of the season after his stay at Southend came to an end.
Southend also have Kacper Lopata on loan from the Blades, while Neal joins him after a successful spell at National League North side Kettering Town.
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The Shrimpers’ connection to Bramall Lane is facilitated by the prescence of Darren Currie at Roots Hall. The nephew of Blades legend Tony, Currie was United’s joint U23s coach last season when Paul Heckingbottom stepped up to take interim charge of the first team and worked with Brunt, Neal and Lopata during his time at Bramall Lane.
“They [United] have been brilliant to deal with," Southend boss Kevin Maher said.
“Paul Heckingbottom and Jack Lester have been first class with us and to have that relationship is great. Darren knows them well, so it’s a good relationship that we have, both ways.
“Harrison’s a great character. Speaking to those at Sheffield United, from what Darren knows about him and from what we've watched of him, there was nothing but good things.
"He’s been playing for Kettering on a regular basis and done ever so well for them. I’m really pleased to get him in and I’m sure he’ll be great for us, the type of character he is and how he goes about his business on the pitch.”