The 25-year-old now needs to build his fitness and will miss the campaign opener with Spurs a week on Saturday.
"He (Valencia) needs to do at least three weeks' work before we'd consider him for the first team," said Allardyce following his side's 7-6 penalty shootout victory over Schalke last night.
"So yes (I want to sign a new striker). I hope it happens before Tottenham, I'm keeping my fingers crossed.
"Everyone is trying extremely hard - especially the chairmen."
For the big stories and the banter follow us on Twitter: @tribalfootball