The Three Lions are only a few days away from beginning their latest quest for continental stardom, although their warm-up period of friendlies was an extremely mixed affair.
After putting three past Bosnia-Herzegovina without reply - rallying in the second half after an uninspiring display in the first period - Southgate's men suffered a chastening 1-0 loss to Iceland at Wembley.
England's friendly defeat to Our Boys came eight years after they suffered a humiliating exit to the Nordic nation at Euro 2016, although they are still regarded as one of the favourites to go all the way in this summer's tournament.
Southgate unsurprisingly chopped and changed his team during their two warm-up matches, which came either side of the Three Lions boss confirming his 26-man selection, several of whom were carrying knocks ahead of the flight to Germany.
Jude Bellingham, Bukayo Saka involved in training
However, every England player was available to Southgate in training on Tuesday, as the Three Lions ramped up their preparations at the Ernst Abbe Sportfeld, their training base in Jena.
As a result, the likes of Jude Bellingham, Bukayo Saka and Luke Shaw were all involved in practice, all three of whom failed to start any of England's friendlies, and Saka was only brought off the bench against Iceland.
The Arsenal man had sustained several niggles throughout the domestic campaign and was thought to be a slight doubt for Serbia, but he will seemingly be fine to start for his country, as will Bellingham.
The Real Madrid man was given an extended break after his successful Champions League exploits with Los Blancos, although Sunday is expected to come too soon for Shaw, who has not played since February owing to a muscle problem.
Lewis Dunk, who missed the defeat to Iceland with a knock, is also set to be available, as are John Stones and Marc Guehi, who suffered ankle and head blows in Friday's friendly.
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With every single one of his troops available, Southgate's XI for the Serbia tie should pick itself, with goalkeeper Jordan Pickford and number nine Harry Kane already shoo-ins at either end of the field.
Stones and Guehi are expected to be fit enough to partner up at the back, where Kyle Walker and Kieran Trippier - still filling in for the stricken Shaw - will also protect Pickford.
A recent report claimed that Trent Alexander-Arnold, who was given the number eight shirt for the Euros, is set to be given the nod in midfield alongside Declan Rice, with Bellingham operating just ahead of them.
After failing to make much of an impact in a central role against Iceland, Phil Foden should be given the nod on the left, as Saka fends off the threat of Cole Palmer to come back on the right wing.