Not sure if you've based your conclusion on those stats or not but they certainly don't support the point you're making.
First of all, you post some stats from
last season as evidence of what he can produce on a good day.
Now, the only possible reason a very fit 27 year old footballer like him could have permanently lost his pace as you claim would be as a result of a very serious injury, or multiple muscle injuries (e.g. Giggs or Owen) The obvious serious injury for Valencia was his broken leg. This happened well over a year before he produced those stats. So if we're seeing acceptable performances almost 18 months after that injury, then we can safely assume the broken leg has nothing to do with his under-par performances this season. In the absence of multiple muscular injuries (which he hasn't had) then there's no plausible reason for him losing his pace, or going through some sort of rapid physical decline.
Based on the stats you yourself posted, we can rule out a physical cause for him playing poorly this season. What the stats
do show, however, is someone who has become reluctant to take his man on, get to the byline and cross into the area. Stats aside, it's really quite obvious from watching him that he's not playing with any confidence. Feck knows how long it will take him to regain that confidence but lost confidence is a lot less of a worry, long-term, than this mythical loss of pace you seem to think is behind all his woes.
Anyway, does this really look like a footballer who's lost his pace?