The Blades star was a notable absentee from his country’s home wins over Estonia and Belarus on Thursday and Sunday, after asking to be omitted from the squad for ‘personal reasons’.
Although those reasons have not been made public, Norwood has continued to play for Chris Wilder’s men as they chase promotion to the Premier League and is expected to partner Scotland’s John Fleck in midfield this weekend when United return to Championship action, hosting Bristol City at Bramall Lane.
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When he confirmed his squad for this month's qualifiers, O'Neill was optimistic that Norwood would be "back with us if not in June, certainly by September".
But after Sunday’s dramatic 2-1 win over Belarus, courtesy of an 87th-minute winner from substitute Josh Magennis of Bolton, O’Neill revealed: "I don't expect Oliver to be available for the games in June.”
Following on from Thursday's 2-0 win over Estonia, O’Neill’s men can enjoy the view from the top of Group C, three points clear of Holland – who have won one and lost one – and Germany, who beat Holland 3-2 in their only qualifier so far.
"The mood in the dressing room is brilliant," O'Neill said. "We're top until June! I know it sounds a bit ridiculous but it's a significant thing because we talk about momentum and that's how you get it. You get positivity.
"The games in June are difficult games but they're easier when you go in with momentum from the two performances and results."