Alves has scored four goals in the Premier League this season
Afonso Alves will miss Middlesbrough's two remaining games this season after breaking his foot in Monday night's 3-1 defeat by Newcastle.
The Brazilian striker was tripped by Nicky Butt after 31 minutes and had to be carried off moments later.
Butt received a yellow card but Boro manager Gareth Southgate pointed to the incident as the game's turning point.
"It was a deliberate foul, it looks like he's broken his foot, it was a big moment in the game," said Southgate.
Alves, who joined Boro from Dutch Eredivisie side Heerenveen for £10m in January 2008, has struggled for form this season but is the club's top scorer with four goals in the Premier League and three in the FA Cup.
Marlon King came on for Alves at St James' Park and is likely to fill the void against Aston Villa on Saturday, and for the trip to West Ham on the last day of the season.
The loss of Alves will be a further blow to a side who are already without captain Emanuel Pogatetz, who will miss the end of the season after knee surgery.
David Wheater (knee) and Didier Digard (groin) are also fitness doubts after missing the Newcastle game.
Boro are now three points from safety with an inferior goal difference to Hull and Newcastle as they look to extend their 11-year stay in the top flight.
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