The Baggies sat third in the Premier League at the start of December but have since won just two of 11 games in all competitions, their latest reverse coming with a 1-0 defeat to QPR in their FA Cup third-round replay on Tuesday night.
Injuries to key players have disrupted Albion's rhythm but Clarke is hopeful midfielder Claudio Yacob and strikers Shane Long and Marc-Antoine Fortune could return for Saturday's West Midlands derby with Aston Villa at The Hawthorns.
Clarke said: "The squad has been stretched to the limit over the last six weeks. The boys that have gone in have done their best. They've tried hard, they've worked.
"Maybe the little bit of luck we were carrying a few weeks ago has deserted us a little bit.
"But all we can do is knuckle down and get on with it. As a group we know what we're trying to do.
"It's a long season and we're going to have moments when things don't go particularly well for you. This is one of those moments.
"We need to get a little bit of rhythm and continuity back into the group. That's the main aim I've got for the next three to four weeks.
"We got Peter Odemwingie and Steven Reid back on the pitch for a few minutes against QPR. Claudio Yacob has trained for a couple of days after his hamstring problem with the group and he's probably 50-50 for Saturday.
"Shane Long's dead leg is improving and again I'd say he's 50-50 for the weekend.
"Marc-Antoine Fortune (hamstring) is maybe a better chance for the weekend, maybe 60-40 in our favour.
"We are hopeful we will have an three or bodies back, if not this weekend then certainly when we go to Everton for the game after that.
"We should more or less be back to full strength given a fair run of no injuries."
Baggies defender Gareth McAuley called on West Brom to bring an end to their five-match winless run in all competitions.
"We've lost a few on the bounce now so we've got to dig deep," he said.
"The senior guys in the squad have to get everyone together and get everyone positive because we have a very important game on Saturday.
"I don't know what's changed. Maybe it's just little bits and piece and the rub of the green here and there.
"We've just got to keep believing because we know it will turn around if we keep doing what we're asked to and perform to our best.
"Villa will be desperate for the points but we're desperate for a performance, for a win and for a clean sheet - for anything at the minute - and there's no better place to do it."