The midfielder hobbled off after 40 minutes of Monday night's Premiership victory at the Lane.
Head Coach Martin said: "Teemu has a bit of a ligament strain in his knee and it could take a week, it could take two weeks.
"I wish him well because he's done well for us lately. He's played on the left and played in the hole against Portsmouth because I thought we needed to pressurise them in the centre.
"He's so aggressive and always gives 100 per cent. Hopefully he'll be back soon."
Martin Jol reports that Teemu Tainio could be out for between one and two weeks with a slight knee injury sustained against Portsmouth.