Initial fears of a break were quickly dispelled and Senior was able to limp into the dressing room at half-time, but he remains a serious doubt for the Millennium Stadium clash with Hull.
"We're hoping it's just a soft-tissue problem but we've got to check it out," said the Leeds coach, Tony Smith. "We're hoping to have a clearer idea in the next 24 hours. He was able to put some weight on it, which is always a good sign."
Senior, a member of the Sheffield Eagles team who famously beat Wigan to lift the cup at Wembley in 1998, has scored 25 tries in 27 appearances for the Rhinos this season and is a key figure in their bid to win the cup.
The Rhinos captain, Kevin Sinfield, just back from a five-week lay-off with a thumb injury, was also in the wars on Friday after picking up a head wound, while their 31-try winger Mark Calderwood missed his first match of the season after failing to recover from a dead leg. But he is expected to return for the trip to Cardiff.
Leeds' hopes of finishing top of the Super League took a severe blow as they were beaten at home for the first time since March. The champions made the ideal start, going ahead through youngster Lee Smith's seventh-minute try, but Bradford's New Zealand Test centre Shontayne Hape scored the first of his three tries on 26 minutes to put his side in front.
The Rhinos trailed 12-10 at half-time and collapsed completely in the second half, conceding six tries, one of them to former captain Iestyn Harris. Bradford's fifth successive win lifted them to third place.
At the other end of the table, winger Tony Stewart claimed his first hat-trick of the season as Salford all but secured their top-flight status with a stunning 37-0 home win over Wakefield. The City Reds ended their four-game losing streak to leapfrog the Wildcats into ninth place and edge Widnes closer to the drop.
The Vikings need to win all their four remaining matches to keep alive their survival chances, starting with the derby clash against Warrington today, although they could yet escape if Gary Hulse and Sala Fa'alogo get their way.
The Widnes duo have joined National League One club Doncaster on loan until the end of the season in an effort to help the Dragons reach October's Grand Final.
The Grand Final winners will be promoted as long as they meet the minimum standards demanded for Super League membership. It is thought Doncaster will fail to meet the criteria by the 31 Aug-ust deadline, unlike fancied pair Castleford and Hull KR.
"We want to help Doncaster win the Grand Final and thereby keep Widnes in Super League," explained the Widnes-born Hulse. "That's our aim."