Pulisic entered the field for the second half, felt discomfort and came off before the start whistle. Chelsea went on to lose 5-2 at Stamford Bridge.
Borussia Dortmund's Reyna, born in England while his father Claudio played for Sunderland, opened the scoring with a deflected strike at Windsor Park.
Premier League: Christian Pulisic says playing in Olympics 'would be amazing,' but admits Chelsea have final say
The United States, who missed out on a place at the 2012 and 2016 Games, have advanced to Sunday's regional qualifying semi-finals, where a victory will secure a place at the Olympics.
Frank Lampard's side suffered a fourth defeat in their last six Premier League games on Sunday as Manchester City eased to a 3-1 win.
Premier League: Chelsea go down against Wolves after conceding in stoppage time; Manchester City draws with West Bromwich
Chelsea missed the chance to climb into first place, at least for one night, while City squandered an opportunity to move within sight of the top two in the division, Tottenham and Liverpool.
Lampard said he enjoyed coaching a player with so much intensity in wanting to perform at the highest level even in the twilight of his career at age 36.
Premier League: Christian Pulisic’s injury a minor one, winger could return for Chelsea by weekend, says Frank Lampard
Lampard said Pulisic would not be available to play against Rennes in the Champions League on Wednesday but was “already back outside” in training.
League Cup: Frank Lampard urges Chelsea winger Callum Hudson-Odoi to prove his worth in rare first-team start
Hudson-Odoi shot to prominence with both Chelsea and England after making his debut for the club in 2018, but a ruptured Achilles tendon last year slowed his progress.
Premier League: Chelsea midfielder Christian Pulisic out for six weeks, could miss start of new season
Christian Pulisic had 11 goals and eight assists in his first season at Chelsea after joining from Borussia Dortmund.
FA Cup: Pierre-Emerick Aubameyang’s brace helps Arsenal clinch 14th title, make last-minute entry into Europa League
It not only sealed Arsenal's fourth FA Cup in seven seasons. but a place in the Europa League, having only finished eighth in the Premier League.
Premier League: Jurgen Klopp's Liverpool beat Chelsea in eight-goal thriller before long-awaited championship celebration
Liverpool ensured the end of their 30-year title drought long ago. Only the three-month delay to the season because of the coronavirus pandemic delayed the coronation.
Premier League: Christian Pulisic has taken his game to another level, says Chelsea boss Frank Lampard
Pulisic’s league tally this season stands at eight goals from 16 starts, raising expectations among fans that he can reach the same level as former club talisman Eden Hazard.
Frenchman Kante picked up a hamstring strain in the second half of Chelsea’s 3-0 win over Watford at Stamford Bridge on Saturday while Croatian Kovacic did not feature last week in the 3-2 defeat at West Ham United after injuring his Achilles.
Liverpool celebrated their first English championship since 1990 after second-place Manchester City lost 2-1 to Chelsea. Eddie Nketiah pounced on a goalkeeping blunder and Joe Willock added his first Premier League goal to give Arsenal a much-needed 2-0 win at Southampton.
Premier League: Chelsea manager Frank Lampard praises Christian Pulisic, Ross Barkley and Cesar Azpilicueta in Aston Villa win
The comeback win for Frank Lampard's club over Aston Villa tightened Chelsea’s grip on fourth place.
Premier League: Faltering restart for Liverpool title charge after shutdown; Chelsea secure comeback win at Aston Villa
With eight games still remaining, Liverpool has plenty of breathing space to end the drought and win its first domestic championship since 1990.
Premier League: Olivier Giroud, Christian Pulisic score in Chelsea win; Newcastle ease past 10-man Sheffield United
The result left Chelsea fourth on 51 points from 30 games, five ahead of fifth-placed Manchester United, while Villa’s hopes of avoiding the drop were dented as they stayed second-bottom on 26 points, one point adrift of the safety zone.
Premier League: Chelsea's Christian Pulisic utilises COVID-19 shutdown to regain to full fitness from adductor injury
Pulisic, who became the most expensive American soccer player when he joined Chelsea in January 2019, has not played since the 1-1 draw against Brighton & Hove Albion on New Year’s Day.
FA Cup: Chelsea boss Frank Lampard laments injuries to key players ahead of crucial fifth-round clash against Liverpool
Players such as midfielder N’Golo Kante have had a stop-start campaign while others like Antonio Rudiger have either returned from injury recently or been sidelined like winger Christian Pulisic
Premier League: Chelsea boss Frank Lampard urges players to put Champions League defeat to Bayern Munich behind them
The 3-0 loss to the German champions at Stamford Bridge in the first leg of their last-16 tie was the heaviest ever defeat for Chelsea in a home game in European competition