Walcott has about an 8 match purple patch each season, where he bangs them in and reminds everyone what a great player he can be, right before breaking down with injury over the Summer, coming back for a short stint at the start of the following season, before getting a lengthy injury that puts him out until after Christmas, which then becomes around Easter. Repeat.
Good player, horrendous injury record. So it's pretty pointless. There's no point valuing him at X amount now, when in a month or two he can just as easily be a wash out for the coming season.