Liverpool dealt Agger and Johnson blow
Denmark international Agger, 26, has been ruled out for the rest of the season after limping off in their 2-1 Premier League defeat by West Bromwich Albion on Saturday.
England right back Johnson, 26, injured his hamstring in the same game and will be out for three to four weeks.
"Daniel has a problem with the tendon behind his knee and won't be involved again this season," manager Kenny Dalglish told the club's website.
Agger is now a doubt for Denmark's Euro 2012 qualifier against Iceland on June 4.
Liverpool are sixth in the Premier League and play third-placed Manchester City at Anfield on Monday.