Arsenal striker Eduardo will miss this Saturday's visit of Blackburn to the Emirates after picking up an injury during the Gunners' defeat of Roma.
The 25-year-old sustained the injury during the first half of extra-time in Rome and went on to miss a penalty in the shoot-out.
The Brazilian-born Croatia international missed 11 months with a broken leg last season, and has now suffered two minor injury setbacks in his bid for full fitness upon his return.
"Unfortunately we have lost Eduardo with a groin problem," Arsenal boss Arsene Wenger told Arsenal TV online.
"He got it in the first half of extra-time and I wonder if that stopped him from taking his penalty that well.
"It shows you that no matter what you do in training when you go to the uncontrolled movements of top, top level competition your body needs time to adjust.
"It is only a short-term injury but he is out for Saturday," added Wenger.