England boss Gareth Southgate has issued a warning to the squad about their futures, citing the omission of veteran Kyle Walker as an example that no player is safe.The Manchester City defender was the surprise snub in the 25-man squad named to face Bulgaria and Kosovo in September’s Euro 2020 qualifiers.Southgate explained that all players in the squad should be wary of their Three Lions futures and if they fail to perform, there is plenty of options, both experienced and young, waiting in the wings for selection. Article continues below Editors’ Picks What is Manchester United’s ownership situation and how would Kevin Glazer’s sale of shares affect the club? Ox-rated! Dream night in Genk for Liverpool ace after injury nightmare Messi a man for all Champions League seasons – but will this really be Barcelona’s? Are Chelsea this season’s Ajax? Super-subs Batshuayi & Pulisic show Blues can dare to dream “That challenge is there for all of them, and whether they are younger or older, don’t assume anything, because I think everyone has to keep performing if we’re to challenge the best teams and that’s how we are going to develop,” Southgate said to reporters.”They’ve got to play well and it’s going to be harder to get in, because you can see the players we’ve had to leave out who’ve got a lot of caps between them, high-level players, we know there are some others around the fringes that could be close.”And we know that there are some more young ones coming that are going to push that as well.”Walker appears to have lost his starting position at right-back to Liverpool’s Trent Alexander-Arnold, with Manchester United’s Aaron Wan-Bissaka and Atletico Madrid’s Kieran Tripper also selected in the squad as right-sided defenders.Southgate was adamant that Walker still had a future at international level, but said there was no point in selecting the 29-year-old when he wasn’t going to start in either match.”Without getting Trent’s [Alexander-Arnold] head too big, too quickly, he’s got to be one of those we look to integrate and give more opportunity to. So, it’s a bit like at a club, if we don’t make a pathway, then when are you ever going to put them in?” he said.”With Aaron [Wan-Bissaka], [we’ve got] a completely different kind of player so we’ve got Trips [Kieran Trippier] as a bit of cover around that and there’s no point bringing Kyle in if the intention is not to start him in the games.”He’s a senior player and he’ll value the rest and recovery as much as anything else. But, we could be in a different space in four weeks’ time because, as I said, he’s started the season very well, he’s obviously got competition for his place at his club, and we’ve got that here.”England’s squad featured four uncapped players, with Wan-Bissaka, James Maddison, Mason Mount and Tyrone Mings all hoping to make their first senior appearances for their nation.The Three Lions will host their first two Euro 2020 qualifiers with the match against Bulgaria played at Wembley on September 7 before welcoming Kosovo three days later at St Mary’s.