The Scotland international midfielder has been an ever-present for the Baggies of late, starting the club's last six Premier League matches.
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Pepe Mel's men sit three points above the relegation zone with four games to play and Olsson told the club's official website: "He's in great shape and doing very well in his last few games.
"It means a lot to have him in good form. We know he can get a few goals, is good on set-pieces, can get assists and has a good work-rate.
"It is good to have him back to his normal self.
"He has had a tough season but he's done very well in the last few weeks."
West Brom's next game is a home fixture against 12th-placed West Ham on Saturday.