No4 was quite commonly worn by midfielders in the past. Muhren wore it for us in the past, more recently Hargreaves and Veron.
Makalele, Rijkard and Pep also wore 4 at times.
Pre premier league era, as I recall, 4s were as common in midfield as 5s and 6s.
Probably this has roots in the traditional numbering where 4, 5 and 6 were the “half backs”. When 442 became the norm, one of these no4, no5 or no6 moved into what we now call midfield (and would have been whichever of those guys was most suited to it and then just keeping the number they already wore). That’s why we got a mix of 4s, 5s and 6s in midfield.