Watford's Dan Gosling faces a lengthy spell on the sidelines after suffering a serious Achilles injury in their game against Bristol City.
Gosling also deputised at full-back for the Hornets earlier in the season.
"It's a disaster. He's a top player, top everything and a great professional," Watford head coach Slaven Bilic told BBC Three Counties.
"When we needed a right-back he stepped in and did a great job.
"Unfortunately it happened and it doesn't look good.
"But we're going to be behind him and hopefully he'll come back soon."
The former Everton and Newcastle player moved to Vicarage Road in 2021 after ending his seven-year stint with Bournemouth.