ajohn

Head pattern and structure show this is a warbler - one of the Phylloscopus.
It's difficult to ID certainly from this photo because many of the useful features aren't visible, but I think is probably a Dusky Warbler (based on the buffy flanks and dark eye-stripe)

ajohn

The bird is in moult, so you can see some of the darker bases to the feathers showing where the overlying feathers are missing. It is not unusual for Dusky Warbler to be in head & body moult at this time of year.