Context : T Cha is a young star surrounded by a cold disk .
The presence of a gap within its disk , inferred from fitting to the spectral energy distribution , has suggested on-going planetary formation .

Aims : The aim of this work is to look for very low-mass companions within the disk gap of T Cha .

Methods : We observed T Cha in L ^ { \prime } and K _ { s } with NAOS-CONICA , the adaptive optics system at the VLT , using sparse aperture masking .

Results : We detected a source in the L ^ { \prime } data at a separation of 62 \pm 7 mas , position angle of \sim 78 \pm 1 degrees , and a contrast of \Delta L ^ { \prime } = 5.1 \pm 0.2 mag .
The object is not detected in the K _ { s } band data , which show a 3- \sigma contrast limit of 5.2 mag at the position of the detected L ^ { \prime } source .
For a distance of 108 pc , the detected companion candidate is located at 6.7 AU from the primary , well within the disk gap .
If T Cha and the companion candidate are bound , the comparison of the L ^ { \prime } and K _ { s } photometry with evolutionary tracks shows that the photometry is inconsistent with any unextincted photosphere at the age and distance of T Cha .
The detected object shows a very red K _ { s } - L ^ { \prime } color for which a possible explanation would be a significant amount of dust around it .
This would imply that the companion candidate is young , which would strengthen the case for a physical companion , and moreover that the object would be in the substellar regime , according to the K _ { s } upper limit .
Another exciting possibility would be that this companion is a recently formed planet within the disk .
Additional observations are mandatory to confirm that the object is bound and to properly characterize it .

Conclusions :