The midfielder made his first international appearance since 2012 as Roy Hodgson's men triumphed 3-1 over Scotland in Glasgow on Tuesday, but came off at the break following an anonymous first half.
However, Allardyce says Downing was carrying an injury and has backed the 30-year-old to enjoy further involvement with the national side.
"He had an injury in the first half which restricted his movement," Allardyce told reporters. "I watched the game and I didn't see him do anything wrong.
"I know people have criticised his performance but I thought he did OK. He certainly hasn't blown his chances of further international call-ups."
Downing is joined in the Upton Park treatment room by Diafra Sakho (back), and both are doubts for Saturday's clash with Everton.
"[Sakho] only got back [from international duty with Senegal] last night so we haven't had time to assess him yet," Allardyce added.
"We'll be looking at him today [Thursday] and make a decision soon. Obviously we don't have too much time before the Everton game on Saturday so it'll be touch and go.
"It's a problem every manager faces after international duty. Stewart Downing came off at half-time with a knee problem as well so we have to monitor that one too.
"They're both two players that have been in top form for us. Sakho's goals and Downing's performances are two of the reasons why we're fourth at the moment.
"We need to be very careful with both players because we don't want to take any risks with their long-term fitness.
If they play on Saturday and aggravate the injury they could be out for two or three weeks which would mean missing five or six games and we can't afford that. We have a tough run of games coming."
Allardyce also revealed Andy Carroll and Carlton Cole are not 100 per cent fit, but will be ready to start against Everton if called upon.
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