Stuart Holden's return to competitive action lasted just 23 minutes last night as he was forced off during an Under-21 match for Bolton Wanderers.
The USA midfielder was playing his first match of the season after seven months out with a cruciate ligament injury.
Holden pulled up with no-one near him during the Under-21 game against Everton at the Reebok Stadium and will now undergo further assessment in the States, the club said.
Before last night's match, Holden tweeted: "Ahhhh butterflies, not had those in a while! A lot of hardwork has gone into this and ready for next step! Thx for all the support."
Holden's last appearance for Bolton's first team was on January 26 last year in an FA Cup tie against Everton.
