Ballard will join Scott Malone, who picked up a hamstring problem against Hull City on Easter Monday, and talisman Jed Wallace on the sidelines, with the latter not yet returning to training following a groin complaint.
Having arrived on loan from Arsenal in the summer after a productive stint at League One promotion winners Blackpool in 2020-21, Ballard has made 33 appearances for the Lions in all competitions this season, scoring once in September’s 1-1 draw away at West Bromwich Albion.
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The 22-year-old Northern Ireland international spent two months on the sidelines between December and February following a knee injury, but aside from that has been a regular in Gary Rowett’s starting 11.
However he will now be absent for at least a week and a half, which means missing this coming weekend’s clash with Peterborough United and a trip to AFC Bournemouth on the final day of the season.
Ballard will be a big miss for the Lions for the final two games of the 2021-22 campaign – and his absence could have severe ramifications on getting a potential play-off spot.
Millwall need to realistically either get four points or win both games and hope other results go their way, and to do that they need their best players available.
Ballard formed part of a solid and reliable trio with Jake Cooper and Murray Wallace in the last few months, but two of those have now been taken away as Wallace has shifted to wing-back in Malone’s absence.
It means that it’s back to the drawing board for Rowett, who need to figure out who will replace Ballard in the starting 11 – whoever it is is not likely to be as good as the Arsenal youngster.