Ecuador international Valencia is poised to join West Ham from Liga MX club Pachuca for a reported fee of £12 million after impressing at the FIFA World Cup in Brazil, with three goals in as many games.
Valencia also topped the scoring charts during the 2014 Liga MX Clausura campaign, netting 12 goals as Pachuca lost to Leon in a two-legged final.
With Argentine forward Mauro Zarate also moving to Upton Park, Downing is hopeful it will help bring out the best in Carroll, who made just 15 Premier League appearances last season due to injuries.
"We can't rely on Andy all season," Downing said.
"He was the big signing last season, but Andy struggled with injuries so hopefully the new signings will take the pressure off him a little bit.
"And from what I've seen of Valencia against England, he looks a very good player.
"He can nick a goal and it is competition for places. It's what we've needed as we didn't have that last season."
